diff --git a/readme.md b/readme.md
index f4af823..7b2a0b4 100755
--- a/readme.md
+++ b/readme.md
@@ -199,6 +199,7 @@ You can run `$INSTALL_DIR/bin/native-platform-test` to run the test application.
   libncurses cannot be loaded.
 * Add a method to Terminal that indicates whether the cursor wraps to the next line when a character is written to the
   rightmost character position.
+* Check for null parameters.
 
 ### Ideas
 
diff --git a/src/main/cpp/win.cpp b/src/main/cpp/win.cpp
index 44bfdf1..1bb4f68 100755
--- a/src/main/cpp/win.cpp
+++ b/src/main/cpp/win.cpp
@@ -109,13 +109,55 @@ Java_net_rubygrapefruit_platform_internal_jni_PosixProcessFunctions_setWorkingDi
     if (dirPath == NULL) {
         return;
     }
-    if (!SetCurrentDirectoryW(dirPath)) {
+    BOOL ok = SetCurrentDirectoryW(dirPath);
+    free(dirPath);
+    if (!ok) {
         mark_failed_with_errno(env, "could not set current directory", result);
-        free(dirPath);
         return;
     }
+}
 
-    free(dirPath);
+JNIEXPORT jstring JNICALL
+Java_net_rubygrapefruit_platform_internal_jni_PosixProcessFunctions_getEnvironmentVariable(JNIEnv *env, jclass target, jstring var, jobject result) {
+    wchar_t* varStr = java_to_wchar(env, var, result);
+    DWORD len = GetEnvironmentVariableW(varStr, NULL, 0);
+    if (len == 0) {
+        if (GetLastError() != ERROR_ENVVAR_NOT_FOUND) {
+            mark_failed_with_errno(env, "could not determine length of environment variable", result);
+        }
+        free(varStr);
+        return NULL;
+    }
+    wchar_t* valueStr = (wchar_t*)malloc(sizeof(wchar_t) * len);
+    DWORD copied = GetEnvironmentVariableW(varStr, valueStr, len);
+    if (copied == 0) {
+        if (len > 1) {
+            // If the value is empty, then copied will be 0
+            mark_failed_with_errno(env, "could not get environment variable", result);
+        }
+        free(varStr);
+        free(valueStr);
+        return NULL;
+    }
+    free(varStr);
+    jstring value = wchar_to_java(env, valueStr, copied, result);
+    free(valueStr);
+    return value;
+}
+
+JNIEXPORT void JNICALL
+Java_net_rubygrapefruit_platform_internal_jni_PosixProcessFunctions_setEnvironmentVariable(JNIEnv *env, jclass target, jstring var, jstring value, jobject result) {
+    wchar_t* varStr = java_to_wchar(env, var, result);
+    wchar_t* valueStr = value == NULL ? NULL : java_to_wchar(env, value, result);
+    BOOL ok = SetEnvironmentVariableW(varStr, valueStr);
+    free(varStr);
+    if (valueStr != NULL) {
+        free(valueStr);
+    }
+    if (!ok && GetLastError() != ERROR_ENVVAR_NOT_FOUND) {
+        mark_failed_with_errno(env, "could not set environment var", result);
+        return;
+    }
 }
 
 /*
diff --git a/src/main/headers/generic.h b/src/main/headers/generic.h
index 1cebf03..6924568 100755
--- a/src/main/headers/generic.h
+++ b/src/main/headers/generic.h
@@ -23,7 +23,7 @@
 extern "C" {
 #endif
 
-#define NATIVE_VERSION 12
+#define NATIVE_VERSION 13
 
 /*
  * Marks the given result as failed, using the given error message
diff --git a/src/main/java/net/rubygrapefruit/platform/Process.java b/src/main/java/net/rubygrapefruit/platform/Process.java
index 6a970fe..956fa29 100755
--- a/src/main/java/net/rubygrapefruit/platform/Process.java
+++ b/src/main/java/net/rubygrapefruit/platform/Process.java
@@ -1,49 +1,68 @@
-/*
- * Copyright 2012 Adam Murdoch
- *
- *    Licensed under the Apache License, Version 2.0 (the "License");
- *    you may not use this file except in compliance with the License.
- *    You may obtain a copy of the License at
- *
- *        http://www.apache.org/licenses/LICENSE-2.0
- *
- *    Unless required by applicable law or agreed to in writing, software
- *    distributed under the License is distributed on an "AS IS" BASIS,
- *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- *    See the License for the specific language governing permissions and
- *    limitations under the License.
- */
-
-package net.rubygrapefruit.platform;
-
-import java.io.File;
-
-/**
- * Functions to query and modify a process' state.
- */
-@ThreadSafe
-public interface Process extends NativeIntegration {
-    /**
-     * Returns the process identifier.
-     *
-     * @throws NativeException On failure.
-     */
-    @ThreadSafe
-    int getProcessId() throws NativeException;
-
-    /**
-     * Returns the process' current working directory.
-     *
-     * @throws NativeException On failure.
-     */
-    @ThreadSafe
-    File getWorkingDirectory() throws NativeException;
-
-    /**
-     * Sets the process' working directory.
-     *
-     * @throws NativeException On failure.
-     */
-    @ThreadSafe
-    void setWorkingDirectory(File directory) throws NativeException;
-}
+/*
+ * Copyright 2012 Adam Murdoch
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+
+package net.rubygrapefruit.platform;
+
+import java.io.File;
+
+/**
+ * Functions to query and modify a process' state.
+ */
+@ThreadSafe
+public interface Process extends NativeIntegration {
+    /**
+     * Returns the process identifier.
+     *
+     * @throws NativeException On failure.
+     */
+    @ThreadSafe
+    int getProcessId() throws NativeException;
+
+    /**
+     * Returns the process' current working directory.
+     *
+     * @throws NativeException On failure.
+     */
+    @ThreadSafe
+    File getWorkingDirectory() throws NativeException;
+
+    /**
+     * Sets the process' working directory.
+     *
+     * @throws NativeException On failure.
+     */
+    @ThreadSafe
+    void setWorkingDirectory(File directory) throws NativeException;
+
+    /**
+     * Get the value of an environment variable.
+     *
+     * @return The value or null if no such environment variable.
+     * @throws NativeException On failure.
+     */
+    @ThreadSafe
+    String getEnvironmentVariable(String name) throws NativeException;
+
+    /**
+     * Sets the value of an environment variable.
+     *
+     * @param value the new value. Use null to remove the environment variable. Note that on some platforms it is not
+     * possible to remove the environment variable. On such platforms, the value is set to an empty string instead.
+     * @throws NativeException On failure.
+     */
+    @ThreadSafe
+    void setEnvironmentVariable(String name, String value) throws NativeException;
+}
diff --git a/src/main/java/net/rubygrapefruit/platform/internal/DefaultProcess.java b/src/main/java/net/rubygrapefruit/platform/internal/DefaultProcess.java
index 17b440f..2471a38 100755
--- a/src/main/java/net/rubygrapefruit/platform/internal/DefaultProcess.java
+++ b/src/main/java/net/rubygrapefruit/platform/internal/DefaultProcess.java
@@ -1,46 +1,79 @@
-/*
- * Copyright 2012 Adam Murdoch
- *
- *    Licensed under the Apache License, Version 2.0 (the "License");
- *    you may not use this file except in compliance with the License.
- *    You may obtain a copy of the License at
- *
- *        http://www.apache.org/licenses/LICENSE-2.0
- *
- *    Unless required by applicable law or agreed to in writing, software
- *    distributed under the License is distributed on an "AS IS" BASIS,
- *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- *    See the License for the specific language governing permissions and
- *    limitations under the License.
- */
-
-package net.rubygrapefruit.platform.internal;
-
-import net.rubygrapefruit.platform.*;
-import net.rubygrapefruit.platform.internal.jni.PosixProcessFunctions;
-
-import java.io.File;
-
-public class DefaultProcess implements net.rubygrapefruit.platform.Process {
-    public int getProcessId() throws NativeException {
-        return PosixProcessFunctions.getPid();
-    }
-
-    public File getWorkingDirectory() throws NativeException {
-        FunctionResult result = new FunctionResult();
-        String dir = PosixProcessFunctions.getWorkingDirectory(result);
-        if (result.isFailed()) {
-            throw new NativeException(String.format("Could not get process working directory: %s", result.getMessage()));
-        }
-        return new File(dir);
-    }
-
-    public void setWorkingDirectory(File directory) throws NativeException {
-        FunctionResult result = new FunctionResult();
-        PosixProcessFunctions.setWorkingDirectory(directory.getAbsolutePath(), result);
-        if (result.isFailed()) {
-            throw new NativeException(String.format("Could not set process working directory: %s", result.getMessage()));
-        }
-        System.setProperty("user.dir", directory.getAbsolutePath());
-    }
-}
+/*
+ * Copyright 2012 Adam Murdoch
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+
+package net.rubygrapefruit.platform.internal;
+
+import net.rubygrapefruit.platform.NativeException;
+import net.rubygrapefruit.platform.Process;
+import net.rubygrapefruit.platform.internal.jni.PosixProcessFunctions;
+
+import java.io.File;
+
+public class DefaultProcess implements Process {
+    private final Object workingDirectoryLock = new Object();
+    private final Object environmentLock = new Object();
+
+    public int getProcessId() throws NativeException {
+        return PosixProcessFunctions.getPid();
+    }
+
+    public File getWorkingDirectory() throws NativeException {
+        FunctionResult result = new FunctionResult();
+        String dir;
+        synchronized (workingDirectoryLock) {
+            dir = PosixProcessFunctions.getWorkingDirectory(result);
+        }
+        if (result.isFailed()) {
+            throw new NativeException(String.format("Could not get process working directory: %s",
+                    result.getMessage()));
+        }
+        return new File(dir);
+    }
+
+    public void setWorkingDirectory(File directory) throws NativeException {
+        FunctionResult result = new FunctionResult();
+        synchronized (workingDirectoryLock) {
+            PosixProcessFunctions.setWorkingDirectory(directory.getAbsolutePath(), result);
+            System.setProperty("user.dir", directory.getAbsolutePath());
+        }
+        if (result.isFailed()) {
+            throw new NativeException(String.format("Could not set process working directory: %s",
+                    result.getMessage()));
+        }
+    }
+
+    public String getEnvironmentVariable(String name) throws NativeException {
+        FunctionResult result = new FunctionResult();
+        String value;
+        synchronized (environmentLock) {
+            value = PosixProcessFunctions.getEnvironmentVariable(name, result);
+        }
+        if (result.isFailed()) {
+            throw new NativeException(String.format("Could not get the value of environment variable '%s': %s", name, result.getMessage()));
+        }
+        return value;
+    }
+
+    public void setEnvironmentVariable(String name, String value) throws NativeException {
+        FunctionResult result = new FunctionResult();
+        synchronized (environmentLock) {
+            PosixProcessFunctions.setEnvironmentVariable(name, value, result);
+        }
+        if (result.isFailed()) {
+            throw new NativeException(String.format("Could not set the value of environment variable '%s': %s", name, result.getMessage()));
+        }
+    }
+}
diff --git a/src/main/java/net/rubygrapefruit/platform/internal/jni/NativeLibraryFunctions.java b/src/main/java/net/rubygrapefruit/platform/internal/jni/NativeLibraryFunctions.java
index 8a2c68a..ddc8da1 100755
--- a/src/main/java/net/rubygrapefruit/platform/internal/jni/NativeLibraryFunctions.java
+++ b/src/main/java/net/rubygrapefruit/platform/internal/jni/NativeLibraryFunctions.java
@@ -1,28 +1,28 @@
-/*
- * Copyright 2012 Adam Murdoch
- *
- *    Licensed under the Apache License, Version 2.0 (the "License");
- *    you may not use this file except in compliance with the License.
- *    You may obtain a copy of the License at
- *
- *        http://www.apache.org/licenses/LICENSE-2.0
- *
- *    Unless required by applicable law or agreed to in writing, software
- *    distributed under the License is distributed on an "AS IS" BASIS,
- *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- *    See the License for the specific language governing permissions and
- *    limitations under the License.
- */
-
-package net.rubygrapefruit.platform.internal.jni;
-
-import net.rubygrapefruit.platform.internal.FunctionResult;
-import net.rubygrapefruit.platform.internal.MutableSystemInfo;
-
-public class NativeLibraryFunctions {
-    public static final int VERSION = 12;
-
-    public static native int getVersion();
-
-    public static native void getSystemInfo(MutableSystemInfo systemInfo, FunctionResult result);
-}
+/*
+ * Copyright 2012 Adam Murdoch
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+
+package net.rubygrapefruit.platform.internal.jni;
+
+import net.rubygrapefruit.platform.internal.FunctionResult;
+import net.rubygrapefruit.platform.internal.MutableSystemInfo;
+
+public class NativeLibraryFunctions {
+    public static final int VERSION = 13;
+
+    public static native int getVersion();
+
+    public static native void getSystemInfo(MutableSystemInfo systemInfo, FunctionResult result);
+}
diff --git a/src/main/java/net/rubygrapefruit/platform/internal/jni/PosixProcessFunctions.java b/src/main/java/net/rubygrapefruit/platform/internal/jni/PosixProcessFunctions.java
index 0110afd..fb724f0 100755
--- a/src/main/java/net/rubygrapefruit/platform/internal/jni/PosixProcessFunctions.java
+++ b/src/main/java/net/rubygrapefruit/platform/internal/jni/PosixProcessFunctions.java
@@ -1,27 +1,31 @@
-/*
- * Copyright 2012 Adam Murdoch
- *
- *    Licensed under the Apache License, Version 2.0 (the "License");
- *    you may not use this file except in compliance with the License.
- *    You may obtain a copy of the License at
- *
- *        http://www.apache.org/licenses/LICENSE-2.0
- *
- *    Unless required by applicable law or agreed to in writing, software
- *    distributed under the License is distributed on an "AS IS" BASIS,
- *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- *    See the License for the specific language governing permissions and
- *    limitations under the License.
- */
-
-package net.rubygrapefruit.platform.internal.jni;
-
-import net.rubygrapefruit.platform.internal.FunctionResult;
-
-public class PosixProcessFunctions {
-    public static native int getPid();
-
-    public static native String getWorkingDirectory(FunctionResult result);
-
-    public static native void setWorkingDirectory(String dir, FunctionResult result);
-}
+/*
+ * Copyright 2012 Adam Murdoch
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+
+package net.rubygrapefruit.platform.internal.jni;
+
+import net.rubygrapefruit.platform.internal.FunctionResult;
+
+public class PosixProcessFunctions {
+    public static native int getPid();
+
+    public static native String getWorkingDirectory(FunctionResult result);
+
+    public static native void setWorkingDirectory(String dir, FunctionResult result);
+
+    public static native String getEnvironmentVariable(String var, FunctionResult result);
+
+    public static native void setEnvironmentVariable(String var, String value, FunctionResult result);
+}
diff --git a/src/test/groovy/net/rubygrapefruit/platform/ProcessTest.groovy b/src/test/groovy/net/rubygrapefruit/platform/ProcessTest.groovy
index 39a7a5a..77b2055 100755
--- a/src/test/groovy/net/rubygrapefruit/platform/ProcessTest.groovy
+++ b/src/test/groovy/net/rubygrapefruit/platform/ProcessTest.groovy
@@ -58,4 +58,79 @@ class ProcessTest extends Specification {
         where:
         dir << ['dir', 'dir\u03b1']
     }
+
+    def "cannot set working directory to a directory that does not exist"() {
+        def newDir = new File(tmpDir.root, "does not exist");
+
+        when:
+        process.workingDirectory = newDir
+
+        then:
+        NativeException e = thrown()
+        e.message.startsWith("Could not set process working directory:")
+    }
+
+    def "can get and set and remove environment variable"() {
+        when:
+        def value = process.getEnvironmentVariable(varName)
+
+        then:
+        value == null
+        System.getenv(varName) == null
+        System.getenv()[varName] == null
+
+        when:
+        process.setEnvironmentVariable(varName, varValue)
+
+        then:
+        process.getEnvironmentVariable(varName) == varValue
+        System.getenv(varName) == varValue
+        System.getenv()[varName] == varValue
+
+        when:
+        process.setEnvironmentVariable(varName, null)
+
+        then:
+        process.getEnvironmentVariable(varName) == null
+        System.getenv(varName) == null
+        System.getenv()[varName] == null
+
+        where:
+        varName              | varValue
+        'TEST_ENV_VAR'       | 'test value'
+        'TEST_ENV_VAR\u03b1' | 'value\u03b2'
+    }
+
+    def "setting environment variable to null or empty string remove the environment variable"() {
+        when:
+        def value = process.getEnvironmentVariable(varName)
+
+        then:
+        value == null
+        System.getenv(varName) == null
+        System.getenv()[varName] == null
+
+        when:
+        process.setEnvironmentVariable(varName, varValue)
+
+        then:
+        process.getEnvironmentVariable(varName) == null
+        System.getenv(varName) == null
+        System.getenv()[varName] == null
+
+        where:
+        varName              | varValue
+        'TEST_ENV_VAR_EMPTY' | ''
+        'TEST_ENV_VAR_NULL'  | null
+    }
+
+    def "can remove environment variable that does not exist"() {
+        assert process.getEnvironmentVariable("TEST_ENV_UNKNOWN") == null
+
+        when:
+        process.setEnvironmentVariable("TEST_ENV_UNKNOWN", null)
+
+        then:
+        notThrown(NativeException)
+    }
 }