diff --git a/README.md b/README.md
index 0c1b32a6e..28ff3e53e 100644
--- a/README.md
+++ b/README.md
@@ -514,4 +514,27 @@ CacheProvider.setCache(new Cache() {
 });
 ```
 
+### Path Function Provider SPI
+
+This SPI allows adding, overriding, and removing the path functions available in the JsonPath path.
+Therefore, change the `PathFunctionProvider` of the `Configuration`.
+
+```java
+String json = "...";
+
+Configuration conf = Configuration.defaultConfiguration().pathFunctionProvider(new DefaultPathFunctionProvider() {
+    @Override
+    public PathFunction newFunction(String name) throws InvalidPathException {
+        if (name.equals("toUpperCase")) {
+            return (currentPath, parent, model, ctx, parameters) -> ((String) model).toUpperCase();
+        }
+        
+        // Fall back to default functions
+        return super.newFunction(name);
+    }
+});
+
+JsonPath.using(conf).parse(json).read("$.store.book[0].author.toUpperCase()").toString(); // NIGEL REES
+```
+
 [![Analytics](https://ga-beacon.appspot.com/UA-54945131-1/jsonpath/index)](https://github.com/igrigorik/ga-beacon)
diff --git a/json-path/src/main/java/com/jayway/jsonpath/Configuration.java b/json-path/src/main/java/com/jayway/jsonpath/Configuration.java
index 69427e1f0..949c9c03f 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/Configuration.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/Configuration.java
@@ -15,8 +15,11 @@
 package com.jayway.jsonpath;
 
 import com.jayway.jsonpath.internal.DefaultsImpl;
+import com.jayway.jsonpath.spi.pathFunction.DefaultPathFunctionProvider;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 import com.jayway.jsonpath.spi.json.JsonProvider;
 import com.jayway.jsonpath.spi.mapper.MappingProvider;
+import com.jayway.jsonpath.spi.pathFunction.PathFunctionProvider;
 
 import java.util.*;
 
@@ -50,16 +53,19 @@ private static Defaults getEffectiveDefaults(){
     private final MappingProvider mappingProvider;
     private final Set<Option> options;
     private final Collection<EvaluationListener> evaluationListeners;
+    private final PathFunctionProvider pathFunctionProvider;
 
-    private Configuration(JsonProvider jsonProvider, MappingProvider mappingProvider, EnumSet<Option> options, Collection<EvaluationListener> evaluationListeners) {
+    private Configuration(JsonProvider jsonProvider, MappingProvider mappingProvider, EnumSet<Option> options, Collection<EvaluationListener> evaluationListeners, PathFunctionProvider pathFunctionProvider) {
         notNull(jsonProvider, "jsonProvider can not be null");
         notNull(mappingProvider, "mappingProvider can not be null");
         notNull(options, "setOptions can not be null");
         notNull(evaluationListeners, "evaluationListeners can not be null");
+        notNull(pathFunctionProvider, "pathFunctionProvider can not be null");
         this.jsonProvider = jsonProvider;
         this.mappingProvider = mappingProvider;
         this.options = Collections.unmodifiableSet(options);
         this.evaluationListeners = Collections.unmodifiableCollection(evaluationListeners);
+        this.pathFunctionProvider = pathFunctionProvider;
     }
 
     /**
@@ -68,7 +74,13 @@ private Configuration(JsonProvider jsonProvider, MappingProvider mappingProvider
      * @return a new configuration
      */
     public Configuration addEvaluationListeners(EvaluationListener... evaluationListener){
-        return Configuration.builder().jsonProvider(jsonProvider).mappingProvider(mappingProvider).options(options).evaluationListener(evaluationListener).build();
+        return Configuration.builder()
+                .jsonProvider(jsonProvider)
+                .mappingProvider(mappingProvider)
+                .options(options)
+                .evaluationListener(evaluationListener)
+                .pathFunctionProvider(pathFunctionProvider)
+                .build();
     }
 
     /**
@@ -77,7 +89,13 @@ public Configuration addEvaluationListeners(EvaluationListener... evaluationList
      * @return a new configuration
      */
     public Configuration setEvaluationListeners(EvaluationListener... evaluationListener){
-        return Configuration.builder().jsonProvider(jsonProvider).mappingProvider(mappingProvider).options(options).evaluationListener(evaluationListener).build();
+        return Configuration.builder()
+                .jsonProvider(jsonProvider)
+                .mappingProvider(mappingProvider)
+                .options(options)
+                .evaluationListener(evaluationListener)
+                .pathFunctionProvider(pathFunctionProvider)
+                .build();
     }
 
     /**
@@ -94,7 +112,13 @@ public Collection<EvaluationListener> getEvaluationListeners(){
      * @return a new configuration
      */
     public Configuration jsonProvider(JsonProvider newJsonProvider) {
-        return Configuration.builder().jsonProvider(newJsonProvider).mappingProvider(mappingProvider).options(options).evaluationListener(evaluationListeners).build();
+        return Configuration.builder()
+                .jsonProvider(newJsonProvider)
+                .mappingProvider(mappingProvider)
+                .options(options)
+                .evaluationListener(evaluationListeners)
+                .pathFunctionProvider(pathFunctionProvider)
+                .build();
     }
 
     /**
@@ -111,7 +135,13 @@ public JsonProvider jsonProvider() {
      * @return a new configuration
      */
     public Configuration mappingProvider(MappingProvider newMappingProvider) {
-        return Configuration.builder().jsonProvider(jsonProvider).mappingProvider(newMappingProvider).options(options).evaluationListener(evaluationListeners).build();
+        return Configuration.builder()
+                .jsonProvider(jsonProvider)
+                .mappingProvider(newMappingProvider)
+                .options(options)
+                .evaluationListener(evaluationListeners)
+                .pathFunctionProvider(pathFunctionProvider)
+                .build();
     }
 
     /**
@@ -122,6 +152,20 @@ public MappingProvider mappingProvider() {
         return mappingProvider;
     }
 
+    public Configuration pathFunctionProvider(PathFunctionProvider newPathFunctionProvider) {
+        return Configuration.builder()
+                .jsonProvider(jsonProvider)
+                .mappingProvider(mappingProvider)
+                .options(options)
+                .evaluationListener(evaluationListeners)
+                .pathFunctionProvider(newPathFunctionProvider)
+                .build();
+    }
+
+    public PathFunctionProvider pathFunctionProvider() {
+        return this.pathFunctionProvider;
+    }
+
     /**
      * Creates a new configuration by adding the new options to the options used in this configuration.
      * @param options options to add
@@ -131,7 +175,13 @@ public Configuration addOptions(Option... options) {
         EnumSet<Option> opts = EnumSet.noneOf(Option.class);
         opts.addAll(this.options);
         opts.addAll(asList(options));
-        return Configuration.builder().jsonProvider(jsonProvider).mappingProvider(mappingProvider).options(opts).evaluationListener(evaluationListeners).build();
+        return Configuration.builder()
+                .jsonProvider(jsonProvider)
+                .mappingProvider(mappingProvider)
+                .options(opts)
+                .evaluationListener(evaluationListeners)
+                .pathFunctionProvider(pathFunctionProvider)
+                .build();
     }
 
     /**
@@ -140,7 +190,13 @@ public Configuration addOptions(Option... options) {
      * @return the new configuration instance
      */
     public Configuration setOptions(Option... options) {
-        return Configuration.builder().jsonProvider(jsonProvider).mappingProvider(mappingProvider).options(options).evaluationListener(evaluationListeners).build();
+        return Configuration.builder()
+                .jsonProvider(jsonProvider)
+                .mappingProvider(mappingProvider)
+                .options(options)
+                .evaluationListener(evaluationListeners)
+                .pathFunctionProvider(pathFunctionProvider)
+                .build();
     }
 
     /**
@@ -186,6 +242,7 @@ public static class ConfigurationBuilder {
         private MappingProvider mappingProvider;
         private EnumSet<Option> options = EnumSet.noneOf(Option.class);
         private Collection<EvaluationListener> evaluationListener = new ArrayList<EvaluationListener>();
+        private PathFunctionProvider pathFunctionProvider = new DefaultPathFunctionProvider();
 
         public ConfigurationBuilder jsonProvider(JsonProvider provider) {
             this.jsonProvider = provider;
@@ -219,6 +276,11 @@ public ConfigurationBuilder evaluationListener(Collection<EvaluationListener> li
             return this;
         }
 
+        public ConfigurationBuilder pathFunctionProvider(PathFunctionProvider pathFunctionProvider) {
+            this.pathFunctionProvider = pathFunctionProvider;
+            return this;
+        }
+
         public Configuration build() {
             if (jsonProvider == null || mappingProvider == null) {
                 final Defaults defaults = getEffectiveDefaults();
@@ -229,7 +291,7 @@ public Configuration build() {
                     mappingProvider = defaults.mappingProvider();
                 }
             }
-            return new Configuration(jsonProvider, mappingProvider, options, evaluationListener);
+            return new Configuration(jsonProvider, mappingProvider, options, evaluationListener, pathFunctionProvider);
         }
     }
 
diff --git a/json-path/src/main/java/com/jayway/jsonpath/JsonPath.java b/json-path/src/main/java/com/jayway/jsonpath/JsonPath.java
index 01c7db03a..401166d68 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/JsonPath.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/JsonPath.java
@@ -18,6 +18,7 @@
 import com.jayway.jsonpath.internal.*;
 import com.jayway.jsonpath.internal.path.PathCompiler;
 import com.jayway.jsonpath.spi.json.JsonProvider;
+import com.jayway.jsonpath.spi.pathFunction.PathFunctionProvider;
 
 import java.io.File;
 import java.io.FileInputStream;
@@ -515,7 +516,6 @@ public static JsonPath compile(String jsonPath, Predicate... filters) {
         return new JsonPath(jsonPath, filters);
     }
 
-
     // --------------------------------------------------------
     //
     // Static utility functions
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PassthruPathFunction.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/PassthruPathFunction.java
index 36d7da77a..a90b27814 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PassthruPathFunction.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/PassthruPathFunction.java
@@ -2,6 +2,7 @@
 
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 
 import java.util.List;
 
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/Append.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/Append.java
index ed39d4a8b..a8c95a2cb 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/Append.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/Append.java
@@ -3,7 +3,7 @@
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 import com.jayway.jsonpath.spi.json.JsonProvider;
 
 import java.util.List;
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/KeySetFunction.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/KeySetFunction.java
index 049d6de0e..3162e3164 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/KeySetFunction.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/KeySetFunction.java
@@ -3,7 +3,7 @@
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 
 import java.util.List;
 
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/numeric/AbstractAggregation.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/numeric/AbstractAggregation.java
index cbc9f7bc9..bc44bf3a4 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/numeric/AbstractAggregation.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/numeric/AbstractAggregation.java
@@ -4,7 +4,7 @@
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 
 import java.util.List;
 
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/sequence/AbstractSequenceAggregation.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/sequence/AbstractSequenceAggregation.java
index 24c87e136..600fc792b 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/sequence/AbstractSequenceAggregation.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/sequence/AbstractSequenceAggregation.java
@@ -4,7 +4,7 @@
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 
 import java.util.ArrayList;
 import java.util.List;
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Concatenate.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Concatenate.java
index d499afef3..cc8e2d2dc 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Concatenate.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Concatenate.java
@@ -3,7 +3,7 @@
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 
 import java.util.List;
 
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Length.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Length.java
index ea8ab1ffe..03b973b18 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Length.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Length.java
@@ -4,7 +4,7 @@
 import com.jayway.jsonpath.internal.Path;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 import com.jayway.jsonpath.internal.path.CompiledPath;
 import com.jayway.jsonpath.internal.path.PathToken;
 import com.jayway.jsonpath.internal.path.RootPathToken;
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/path/EvaluationContextImpl.java b/json-path/src/main/java/com/jayway/jsonpath/internal/path/EvaluationContextImpl.java
index d3fd0b1c6..bf8574c7d 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/path/EvaluationContextImpl.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/path/EvaluationContextImpl.java
@@ -23,6 +23,7 @@
 import com.jayway.jsonpath.internal.Path;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.spi.json.JsonProvider;
+import com.jayway.jsonpath.spi.pathFunction.PathFunctionProvider;
 
 import java.util.ArrayList;
 import java.util.Collection;
@@ -98,6 +99,7 @@ public void addResult(String path, PathRef operation, Object model) {
         }
     }
 
+    public PathFunctionProvider functionProvider() { return configuration.pathFunctionProvider(); }
 
     public JsonProvider jsonProvider() {
         return configuration.jsonProvider();
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/path/FunctionPathToken.java b/json-path/src/main/java/com/jayway/jsonpath/internal/path/FunctionPathToken.java
index 0f4498958..592b910a9 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/path/FunctionPathToken.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/path/FunctionPathToken.java
@@ -3,17 +3,18 @@
 import com.jayway.jsonpath.internal.Path;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
-import com.jayway.jsonpath.internal.function.PathFunctionFactory;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 import com.jayway.jsonpath.internal.function.latebinding.JsonLateBindingValue;
 import com.jayway.jsonpath.internal.function.latebinding.PathLateBindingValue;
+import com.jayway.jsonpath.spi.pathFunction.PathFunctionProvider;
 
 import java.util.List;
+import java.util.Map;
 
 /**
- * Token representing a Function call to one of the functions produced via the FunctionFactory
+ * Token representing a Function call to one of the functions produced via the FunctionProvider
  *
- * @see PathFunctionFactory
+ * @see PathFunctionProvider
  *
  * Created by mattg on 6/27/15.
  */
@@ -22,6 +23,7 @@ public class FunctionPathToken extends PathToken {
     private final String functionName;
     private final String pathFragment;
     private List<Parameter> functionParams;
+    private Map<String, Class<? extends PathFunction>> customFunctions;
 
     public FunctionPathToken(String pathFragment, List<Parameter> parameters) {
         this.pathFragment = pathFragment + ((parameters != null && parameters.size() > 0) ? "(...)" : "()");
@@ -36,7 +38,7 @@ public FunctionPathToken(String pathFragment, List<Parameter> parameters) {
 
     @Override
     public void evaluate(String currentPath, PathRef parent, Object model, EvaluationContextImpl ctx) {
-        PathFunction pathFunction = PathFunctionFactory.newFunction(functionName);
+        PathFunction pathFunction = ctx.functionProvider().newFunction(functionName);
         evaluateParameters(currentPath, parent, model, ctx);
         Object result = pathFunction.invoke(currentPath, parent, model, ctx, functionParams);
         ctx.addResult(currentPath + "." + functionName, parent, result);
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathCompiler.java b/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathCompiler.java
index 27b6e0633..63554668c 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathCompiler.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathCompiler.java
@@ -8,11 +8,9 @@
 import com.jayway.jsonpath.internal.filter.FilterCompiler;
 import com.jayway.jsonpath.internal.function.ParamType;
 import com.jayway.jsonpath.internal.function.Parameter;
+import com.jayway.jsonpath.spi.pathFunction.PathFunctionProvider;
 
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.LinkedList;
-import java.util.List;
+import java.util.*;
 
 import static java.lang.Character.isDigit;
 import static java.util.Arrays.asList;
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathToken.java b/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathToken.java
index 34cf1402b..1d4f158d4 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathToken.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathToken.java
@@ -18,7 +18,7 @@
 import com.jayway.jsonpath.PathNotFoundException;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.Utils;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 import com.jayway.jsonpath.spi.json.JsonProvider;
 
 import java.util.List;
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java b/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/DefaultPathFunctionProvider.java
similarity index 54%
rename from json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
rename to json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/DefaultPathFunctionProvider.java
index 3a31151f2..646059efd 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/DefaultPathFunctionProvider.java
@@ -1,13 +1,9 @@
-package com.jayway.jsonpath.internal.function;
+package com.jayway.jsonpath.spi.pathFunction;
 
 import com.jayway.jsonpath.InvalidPathException;
 import com.jayway.jsonpath.internal.function.json.Append;
 import com.jayway.jsonpath.internal.function.json.KeySetFunction;
-import com.jayway.jsonpath.internal.function.numeric.Average;
-import com.jayway.jsonpath.internal.function.numeric.Max;
-import com.jayway.jsonpath.internal.function.numeric.Min;
-import com.jayway.jsonpath.internal.function.numeric.StandardDeviation;
-import com.jayway.jsonpath.internal.function.numeric.Sum;
+import com.jayway.jsonpath.internal.function.numeric.*;
 import com.jayway.jsonpath.internal.function.sequence.First;
 import com.jayway.jsonpath.internal.function.sequence.Index;
 import com.jayway.jsonpath.internal.function.sequence.Last;
@@ -18,21 +14,12 @@
 import java.util.HashMap;
 import java.util.Map;
 
-/**
- * Implements a factory that given a name of the function will return the Function implementation, or null
- * if the value is not obtained.
- *
- * Leverages the function's name in order to determine which function to execute which is maintained internally
- * here via a static map
- *
- */
-public class PathFunctionFactory {
-
-    public static final Map<String, Class> FUNCTIONS;
+public class DefaultPathFunctionProvider implements PathFunctionProvider {
+    public static final Map<String, Class<? extends PathFunction>> DEFAULT_FUNCTIONS;
 
     static {
         // New functions should be added here and ensure the name is not overridden
-        Map<String, Class> map = new HashMap<String, Class>();
+        Map<String, Class<? extends PathFunction>> map = new HashMap<>();
 
         // Math Functions
         map.put("avg", Average.class);
@@ -49,37 +36,24 @@ public class PathFunctionFactory {
         map.put("size", Length.class);
         map.put("append", Append.class);
         map.put("keys", KeySetFunction.class);
-        
+
         // Sequential Functions
         map.put("first", First.class);
         map.put("last", Last.class);
         map.put("index", Index.class);
 
 
-        FUNCTIONS = Collections.unmodifiableMap(map);
+        DEFAULT_FUNCTIONS = Collections.unmodifiableMap(map);
     }
 
-    /**
-     * Returns the function by name or throws InvalidPathException if function not found.
-     *
-     * @see #FUNCTIONS
-     * @see PathFunction
-     *
-     * @param name
-     *      The name of the function
-     *
-     * @return
-     *      The implementation of a function
-     *
-     * @throws InvalidPathException
-     */
-    public static PathFunction newFunction(String name) throws InvalidPathException {
-        Class functionClazz = FUNCTIONS.get(name);
+    @Override
+    public PathFunction newFunction(String name) throws InvalidPathException {
+        Class<? extends PathFunction> functionClazz = DEFAULT_FUNCTIONS.get(name);
         if(functionClazz == null){
             throw new InvalidPathException("Function with name: " + name + " does not exist.");
         } else {
             try {
-                return (PathFunction)functionClazz.newInstance();
+                return functionClazz.getDeclaredConstructor().newInstance();
             } catch (Exception e) {
                 throw new InvalidPathException("Function of name: " + name + " cannot be created", e);
             }
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunction.java b/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/PathFunction.java
similarity index 92%
rename from json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunction.java
rename to json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/PathFunction.java
index ac3a353ba..585c96471 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunction.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/PathFunction.java
@@ -1,7 +1,8 @@
-package com.jayway.jsonpath.internal.function;
+package com.jayway.jsonpath.spi.pathFunction;
 
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
+import com.jayway.jsonpath.internal.function.Parameter;
 
 import java.util.List;
 
diff --git a/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/PathFunctionProvider.java b/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/PathFunctionProvider.java
new file mode 100644
index 000000000..210da9e5f
--- /dev/null
+++ b/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/PathFunctionProvider.java
@@ -0,0 +1,22 @@
+package com.jayway.jsonpath.spi.pathFunction;
+
+import com.jayway.jsonpath.InvalidPathException;
+
+public interface PathFunctionProvider {
+
+    /**
+     * Returns the function by name or throws InvalidPathException if function not found.
+     *
+     * @see DefaultPathFunctionProvider#DEFAULT_FUNCTIONS
+     * @see PathFunction
+     *
+     * @param name
+     *      The name of the function
+     *
+     * @return
+     *      The implementation of a function
+     *
+     * @throws InvalidPathException
+     */
+    public PathFunction newFunction(String name) throws InvalidPathException;
+}
diff --git a/json-path/src/test/java/com/jayway/jsonpath/CustomPathFunctionTest.java b/json-path/src/test/java/com/jayway/jsonpath/CustomPathFunctionTest.java
new file mode 100644
index 000000000..436f3ce70
--- /dev/null
+++ b/json-path/src/test/java/com/jayway/jsonpath/CustomPathFunctionTest.java
@@ -0,0 +1,44 @@
+package com.jayway.jsonpath;
+
+import com.jayway.jsonpath.internal.function.BaseFunctionTest;
+import com.jayway.jsonpath.spi.pathFunction.DefaultPathFunctionProvider;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunctionProvider;
+import org.junit.jupiter.api.Test;
+
+import static com.jayway.jsonpath.Configurations.JSON_ORG_CONFIGURATION;
+import static com.jayway.jsonpath.JsonPath.using;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class CustomPathFunctionTest extends BaseFunctionTest {
+
+    @Test
+    void testCustomPathFunction() {
+        Configuration conf = Configuration.defaultConfiguration().pathFunctionProvider(new DefaultPathFunctionProvider() {
+            @Override
+            public PathFunction newFunction(String name) throws InvalidPathException {
+                if (name.equals("toUpperCase")) {
+                    return (currentPath, parent, model, ctx, parameters) -> ((String) model).toUpperCase();
+                }
+                return super.newFunction(name);
+            }
+        });
+        verifyTextFunction(conf,"$['text'][0].toUpperCase()","A");
+
+        // Make sure default configuration is not being overwritten
+        assertThrows(InvalidPathException.class, () -> {
+            using(JSON_ORG_CONFIGURATION).parse(TEXT_SERIES).read("$['text'][0].toUpperCase()");
+        });
+    }
+
+    @Test
+    void removeAllPathFunctions() {
+        Configuration conf = Configuration.defaultConfiguration().pathFunctionProvider(name -> {
+            throw new InvalidPathException("No JsonPath functions allowed");
+        });
+        verifyMathFunction(JSON_ORG_CONFIGURATION, "$['empty'].length()", 0);
+        assertThrows(InvalidPathException.class, () -> {
+            using(conf).parse(NUMBER_SERIES).read("$['empty'].length()");
+        });
+    }
+}