diff --git a/pitest-entry/src/main/java/org/pitest/classpath/DefaultCodeSource.java b/pitest-entry/src/main/java/org/pitest/classpath/DefaultCodeSource.java
index c9fdc61b6..469681ba1 100644
--- a/pitest-entry/src/main/java/org/pitest/classpath/DefaultCodeSource.java
+++ b/pitest-entry/src/main/java/org/pitest/classpath/DefaultCodeSource.java
@@ -8,6 +8,7 @@
 import org.pitest.functional.Streams;
 
 import java.util.Collection;
+import java.util.HashSet;
 import java.util.Optional;
 import java.util.Set;
 import java.util.stream.Collectors;
@@ -36,7 +37,7 @@ public Stream<ClassTree> codeTrees() {
     }
 
     public Set<ClassName> getCodeUnderTestNames() {
-        return this.classPath.code().stream().collect(Collectors.toSet());
+        return new HashSet<>(this.classPath.code());
     }
 
     public Set<ClassName> getTestClassNames() {
diff --git a/pitest-entry/src/main/java/org/pitest/mutationtest/config/ReportOptions.java b/pitest-entry/src/main/java/org/pitest/mutationtest/config/ReportOptions.java
index 723eaf20d..843fb8b9d 100644
--- a/pitest-entry/src/main/java/org/pitest/mutationtest/config/ReportOptions.java
+++ b/pitest-entry/src/main/java/org/pitest/mutationtest/config/ReportOptions.java
@@ -33,12 +33,12 @@
 import org.pitest.util.Verbosity;
 
 import java.io.File;
-import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.io.Reader;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -502,8 +502,7 @@ public Optional<Reader> createHistoryReader() {
     try {
       if (this.historyInputLocation.exists()
           && (this.historyInputLocation.length() > 0)) {
-        return Optional.ofNullable(new InputStreamReader(new FileInputStream(
-            this.historyInputLocation), StandardCharsets.UTF_8));
+        return Optional.of(new InputStreamReader(Files.newInputStream(this.historyInputLocation.toPath()), StandardCharsets.UTF_8));
       }
       return Optional.empty();
     } catch (final IOException ex) {
diff --git a/pitest-entry/src/main/java/org/pitest/mutationtest/tooling/EntryPoint.java b/pitest-entry/src/main/java/org/pitest/mutationtest/tooling/EntryPoint.java
index 973aad398..75be0707f 100644
--- a/pitest-entry/src/main/java/org/pitest/mutationtest/tooling/EntryPoint.java
+++ b/pitest-entry/src/main/java/org/pitest/mutationtest/tooling/EntryPoint.java
@@ -111,6 +111,7 @@ public AnalysisResult execute(File baseDir, ReportOptions data,
     final LaunchOptions launchOptions = new LaunchOptions(ja,
         settings.getJavaExecutable(), createJvmArgs(data), environmentVariables)
         .usingClassPathJar(data.useClasspathJar());
+
     final ProjectClassPaths cps = data.getMutationClassPaths();
 
     final CodeSource code = settings.createCodeSource(cps);
diff --git a/pitest-maven-verification/src/test/resources/pit-cross-module-tests/pom.xml b/pitest-maven-verification/src/test/resources/pit-cross-module-tests/pom.xml
index d98c8fbd6..dba85b996 100644
--- a/pitest-maven-verification/src/test/resources/pit-cross-module-tests/pom.xml
+++ b/pitest-maven-verification/src/test/resources/pit-cross-module-tests/pom.xml
@@ -6,13 +6,13 @@
 	<packaging>pom</packaging>
 	<version>1.0-SNAPSHOT</version>
 	<name>pit-parent-module</name>
-	<dependencies>
-		<dependency>
-			<groupId>junit</groupId>
-			<artifactId>junit</artifactId>
-			<version>${junit.version}</version>
-		</dependency>
-	</dependencies>
+
+	<properties>
+		<junit.version>4.13.1</junit.version>
+		<pit.version>dev-SNAPSHOT</pit.version>
+	</properties>
+
+
 	<build>
 		<plugins>
 			<plugin>
@@ -33,6 +33,7 @@
 					<artifactId>pitest-maven</artifactId>
 					<version>${pit.version}</version>
 					<configuration>
+						<crossModule>true</crossModule>
 						<timestampedReports>false</timestampedReports>
 						<outputFormats>
 							<outputFormat>HTML</outputFormat>
@@ -46,12 +47,39 @@
 				</plugin>
 			</plugins>
 		</pluginManagement>
+
 	</build>
 
-	
-	<properties>
-		<junit.version>4.13.1</junit.version>
-	</properties>
+	<profiles>
+		<profile>
+			<id>pitest</id>
+			<build>
+				<plugins>
+					<plugin>
+						<groupId>org.pitest</groupId>
+						<artifactId>pitest-maven</artifactId>
+						<executions>
+							<execution>
+								<id>pitest</id>
+								<phase>test-compile</phase>
+								<goals>
+									<goal>mutationCoverage</goal>
+								</goals>
+							</execution>
+						</executions>
+					</plugin>
+				</plugins>
+			</build>
+		</profile>
+	</profiles>
+	<dependencies>
+		<dependency>
+			<groupId>junit</groupId>
+			<artifactId>junit</artifactId>
+			<version>${junit.version}</version>
+		</dependency>
+	</dependencies>
+
 	<modules>
 	   <module>cross-tests-code</module>
 	   <module>cross-tests-tests</module>
diff --git a/pitest-maven/src/main/java/org/pitest/maven/AbstractPitMojo.java b/pitest-maven/src/main/java/org/pitest/maven/AbstractPitMojo.java
index 514c3198b..f2560cc0f 100644
--- a/pitest-maven/src/main/java/org/pitest/maven/AbstractPitMojo.java
+++ b/pitest-maven/src/main/java/org/pitest/maven/AbstractPitMojo.java
@@ -332,6 +332,13 @@ public class AbstractPitMojo extends AbstractMojo {
   @Parameter(property = "skipTests", defaultValue = "false")
   private boolean                     skipTests;
 
+  /**
+   * Mutate code outside current module
+   */
+  @Parameter(property = "crossModule", defaultValue = "false")
+  private boolean                     crossModule;
+
+
   /**
    * When set will ignore failing tests when computing coverage. Otherwise, the
    * run will fail. If parseSurefireConfig is true, will be overridden from
@@ -739,7 +746,7 @@ protected RunDecision shouldRun() {
       decision.addReason("Packaging is POM.");
     }
 
-    if (!notEmptyProject.test(project)) {
+    if (!notEmptyProject.test(project) && !crossModule) {
       decision.addReason("Project has either no tests or no production code.");
     }
 
@@ -816,6 +823,14 @@ public RepositorySystem repositorySystem() {
     return repositorySystem;
   }
 
+  public boolean isCrossModule() {
+    return crossModule;
+  }
+
+  public List<MavenProject> allProjects() {
+    return session.getProjects();
+  }
+
   static class RunDecision {
     private List<String> reasons = new ArrayList<>(4);
 
diff --git a/pitest-maven/src/main/java/org/pitest/maven/MojoToReportOptionsConverter.java b/pitest-maven/src/main/java/org/pitest/maven/MojoToReportOptionsConverter.java
index 7ea345b49..b90da4f20 100644
--- a/pitest-maven/src/main/java/org/pitest/maven/MojoToReportOptionsConverter.java
+++ b/pitest-maven/src/main/java/org/pitest/maven/MojoToReportOptionsConverter.java
@@ -16,6 +16,7 @@
 
 import org.apache.maven.artifact.Artifact;
 import org.apache.maven.artifact.DependencyResolutionRequiredException;
+import org.apache.maven.model.Build;
 import org.apache.maven.model.Plugin;
 import org.apache.maven.plugin.logging.Log;
 import org.apache.maven.project.MavenProject;
@@ -43,18 +44,20 @@
 import java.util.Enumeration;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Objects;
 import java.util.Optional;
 import java.util.Properties;
 import java.util.Set;
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 import static org.pitest.functional.Streams.asStream;
 
 public class MojoToReportOptionsConverter {
 
-  private final AbstractPitMojo                 mojo;
+  private final AbstractPitMojo         mojo;
   private final Predicate<Artifact>     dependencyFilter;
   private final Log                     log;
   private final SurefireConfigConverter surefireConverter;
@@ -85,6 +88,8 @@ public ReportOptions convert() {
     autoAddJUnitPlatform(classPath);
     removeExcludedDependencies(classPath);
 
+    addCrossModuleDirsToClasspath(classPath);
+
     ReportOptions option = parseReportOptions(classPath);
     ReportOptions withSureFire = updateFromSurefire(option);
 
@@ -100,6 +105,15 @@ public ReportOptions convert() {
 
   }
 
+  private void addCrossModuleDirsToClasspath(List<String> classPath) {
+    // Add the output directories modules we depend on to the start of the classpath.
+    // If we resolve cross project classes from a jar, the path match
+    // will fail. This is only an issue when running the pitest goal directly.
+    if (mojo.isCrossModule()) {
+      classPath.addAll(0, crossModuleDependencies());
+    }
+  }
+
   /**
    * The junit 5 plugin needs junit-platform-launcher to run, but this will not be on the classpath
    * of the project. We want to use the same version that surefire (and therefore the SUT) uses, not
@@ -176,10 +190,22 @@ private ReportOptions parseReportOptions(final List<String> classPath) {
     final ReportOptions data = new ReportOptions();
 
     if (this.mojo.getProject().getBuild() != null) {
+
+      List<String> codePaths = new ArrayList<>();
+      codePaths.add(this.mojo.getProject().getBuild()
+              .getOutputDirectory());
+
+      if (mojo.isCrossModule()) {
+        codePaths.addAll(crossModuleDependencies());
+      }
+
       this.log.info("Mutating from "
-          + this.mojo.getProject().getBuild().getOutputDirectory());
+              + String.join(",", codePaths));
+
       data.setCodePaths(Collections.singleton(this.mojo.getProject().getBuild()
           .getOutputDirectory()));
+
+      data.setCodePaths(codePaths);
     }
 
     data.setUseClasspathJar(this.mojo.isUseClasspathJar());
@@ -215,9 +241,7 @@ private ReportOptions parseReportOptions(final List<String> classPath) {
       data.setLoggingClasses(this.mojo.getAvoidCallsTo());
     }
 
-    final List<String> sourceRoots = new ArrayList<>();
-    sourceRoots.addAll(this.mojo.getProject().getCompileSourceRoots());
-    sourceRoots.addAll(this.mojo.getProject().getTestCompileSourceRoots());
+    final List<String> sourceRoots = determineSourceRoots();
 
     data.setSourceDirs(stringsToPaths(sourceRoots));
 
@@ -253,6 +277,41 @@ private ReportOptions parseReportOptions(final List<String> classPath) {
     return data;
   }
 
+  private List<String> determineSourceRoots() {
+    final List<String> sourceRoots = new ArrayList<>();
+    sourceRoots.addAll(this.mojo.getProject().getCompileSourceRoots());
+    sourceRoots.addAll(this.mojo.getProject().getTestCompileSourceRoots());
+    if (mojo.isCrossModule()) {
+      List<String> otherRoots = dependedOnProjects().stream()
+              .flatMap(p -> p.getCompileSourceRoots().stream())
+              .collect(Collectors.toList());
+
+      sourceRoots.addAll(otherRoots);
+    }
+    return sourceRoots;
+  }
+
+  private Collection<String> crossModuleDependencies() {
+    return dependedOnProjects().stream()
+            .map(MavenProject::getBuild)
+            .map(Build::getOutputDirectory)
+            .filter(Objects::nonNull)
+            .collect(Collectors.toList());
+  }
+
+  private List<MavenProject> dependedOnProjects() {
+    // strip version from dependencies
+    Set<String> inScope = this.mojo.getProject().getDependencies().stream()
+            .map(p -> p.getGroupId() + ":" + p.getArtifactId())
+            .collect(Collectors.toSet());
+
+
+    return this.mojo.allProjects().stream()
+            .filter(p -> inScope.contains(p.getGroupId() + ":" + p.getArtifactId()))
+            .collect(Collectors.toList());
+
+  }
+
   private void configureVerbosity(ReportOptions data) {
     if (this.mojo.isVerbose()) {
       data.setVerbosity(Verbosity.VERBOSE);
@@ -384,6 +443,8 @@ private Collection<String> useConfiguredTargetTestsOrFindOccupiedPackages(
   }
 
   private Collection<String> findOccupiedTestPackages() {
+    // use only the tests within current project, even if in
+    // cross module mode
     String outputDirName = this.mojo.getProject().getBuild()
         .getTestOutputDirectory();
     if (outputDirName != null) {
@@ -430,10 +491,12 @@ private Collection<String> useConfiguredTargetClassesOrFindOccupiedPackages(
   }
 
   private Collection<String> findOccupiedPackages() {
-    String outputDirName = this.mojo.getProject().getBuild()
-        .getOutputDirectory();
-    File outputDir = new File(outputDirName);
-    return findOccupiedPackagesIn(outputDir);
+    return Stream.concat(Stream.of(mojo.getProject()), dependedOnProjects().stream())
+            .distinct()
+            .map(p -> new File(p.getBuild().getOutputDirectory()))
+            .flatMap(f -> findOccupiedPackagesIn(f).stream())
+            .distinct()
+            .collect(Collectors.toList());
   }
   
   public static Collection<String> findOccupiedPackagesIn(File dir) {
diff --git a/pitest-maven/src/test/java/org/pitest/maven/BasePitMojoTest.java b/pitest-maven/src/test/java/org/pitest/maven/BasePitMojoTest.java
index 21419f6de..204c74e91 100644
--- a/pitest-maven/src/test/java/org/pitest/maven/BasePitMojoTest.java
+++ b/pitest-maven/src/test/java/org/pitest/maven/BasePitMojoTest.java
@@ -27,6 +27,7 @@
 import java.util.stream.Collectors;
 
 import org.apache.maven.artifact.Artifact;
+import org.apache.maven.execution.MavenSession;
 import org.apache.maven.model.Build;
 import org.apache.maven.plugin.testing.AbstractMojoTestCase;
 import org.apache.maven.project.MavenProject;
@@ -45,6 +46,9 @@ public abstract class BasePitMojoTest extends AbstractMojoTestCase {
   @Mock
   protected MavenProject        project;
 
+  @Mock
+  protected MavenSession        session;
+
   @Mock
   protected RunPitStrategy      executionStrategy;
 
@@ -118,6 +122,7 @@ protected void configurePitMojo(final AbstractPitMojo pitMojo, final String conf
     setVariableValueToObject(pitMojo, "pluginArtifactMap", pluginArtifacts);
 
     setVariableValueToObject(pitMojo, "project", this.project);
+    setVariableValueToObject(pitMojo, "session", this.session);
 
     if (pitMojo.getAdditionalClasspathElements() == null) {
       ArrayList<String> elements = new ArrayList<>();
diff --git a/pitest-maven/src/test/java/org/pitest/maven/MojoToReportOptionsConverterTest.java b/pitest-maven/src/test/java/org/pitest/maven/MojoToReportOptionsConverterTest.java
index 7edcf0798..3b741cc1c 100644
--- a/pitest-maven/src/test/java/org/pitest/maven/MojoToReportOptionsConverterTest.java
+++ b/pitest-maven/src/test/java/org/pitest/maven/MojoToReportOptionsConverterTest.java
@@ -17,23 +17,20 @@
 import org.apache.maven.artifact.Artifact;
 import org.apache.maven.artifact.DependencyResolutionRequiredException;
 import org.apache.maven.model.Build;
+import org.apache.maven.model.Dependency;
 import org.apache.maven.model.Model;
 import org.apache.maven.model.Plugin;
+import org.apache.maven.project.MavenProject;
 import org.codehaus.plexus.util.xml.Xpp3Dom;
-import org.junit.rules.TemporaryFolder;
 import org.mockito.Mockito;
 import org.pitest.mutationtest.config.ConfigOption;
 import org.pitest.mutationtest.config.ReportOptions;
 import org.pitest.util.Unchecked;
 
 import java.io.File;
-import java.io.IOException;
 import java.nio.charset.StandardCharsets;
-import java.nio.file.Files;
-import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
@@ -41,6 +38,7 @@
 import java.util.Set;
 import java.util.function.Predicate;
 
+import static java.util.Arrays.asList;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatCode;
 import static org.mockito.AdditionalAnswers.returnsFirstArg;
@@ -92,9 +90,9 @@ public void testCreatesPredicateFromListOfTargetClassGlobs() {
   }
 
   public void testUsesSourceDirectoriesFromProject() {
-    when(this.project.getCompileSourceRoots()).thenReturn(Arrays.asList("src"));
+    when(this.project.getCompileSourceRoots()).thenReturn(asList("src"));
     when(this.project.getTestCompileSourceRoots()).thenReturn(
-        Arrays.asList("tst"));
+        asList("tst"));
     final ReportOptions actual = parseConfig("");
     assertThat(actual.getSourcePaths()).containsExactly(Paths.get("src"), Paths.get("tst"));
   }
@@ -125,7 +123,7 @@ public void testParsesListOfMutationOperators() {
         "                      <param>bar</param>" + //
         "                  </mutators>";
     final ReportOptions actual = parseConfig(xml);
-    assertEquals(Arrays.asList("foo", "bar"), actual.getMutators());
+    assertEquals(asList("foo", "bar"), actual.getMutators());
   }
   
   public void testParsesListOfFeatures() {
@@ -205,7 +203,7 @@ public void testParsesListOfClassesToAvoidCallTo() {
         "                      <param>foo.bar</param>" + //
         "                  </avoidCallsTo>";
     final ReportOptions actual = parseConfig(xml);
-    assertEquals(Arrays.asList("foo", "bar", "foo.bar"),
+    assertEquals(asList("foo", "bar", "foo.bar"),
         actual.getLoggingClasses());
   }
 
@@ -244,7 +242,7 @@ public void testParsesDetectInlineCodeFlag() {
 
   public void testDefaultsToHtmlReportWhenNoOutputFormatsSpecified() {
     final ReportOptions actual = parseConfig("");
-    assertEquals(new HashSet<>(Arrays.asList("HTML")),
+    assertEquals(new HashSet<>(asList("HTML")),
         actual.getOutputFormats());
   }
 
@@ -254,7 +252,7 @@ public void testParsesListOfOutputFormatsWhenSupplied() {
         "                      <param>CSV</param>" + //
         "                  </outputFormats>";
     final ReportOptions actual = parseConfig(xml);
-    assertEquals(new HashSet<>(Arrays.asList("HTML", "CSV")),
+    assertEquals(new HashSet<>(asList("HTML", "CSV")),
         actual.getOutputFormats());
   }
 
@@ -276,19 +274,19 @@ public void testObeysSkipFailingTestsFlagWhenPackagingTypeIsNotPOM() {
 
   public void testParsesTestGroupsToExclude() {
     final ReportOptions actual = parseConfig("<excludedGroups><value>foo</value><value>bar</value></excludedGroups>");
-    assertEquals(Arrays.asList("foo", "bar"), actual.getGroupConfig()
+    assertEquals(asList("foo", "bar"), actual.getGroupConfig()
         .getExcludedGroups());
   }
 
   public void testParsesTestGroupsToInclude() {
     final ReportOptions actual = parseConfig("<includedGroups><value>foo</value><value>bar</value></includedGroups>");
-    assertEquals(Arrays.asList("foo", "bar"), actual.getGroupConfig()
+    assertEquals(asList("foo", "bar"), actual.getGroupConfig()
         .getIncludedGroups());
   }
 
   public void testParsesTestMethodsToInclude() {
     final ReportOptions actual = parseConfig("<includedTestMethods><value>foo</value><value>bar</value></includedTestMethods>");
-    assertEquals(Arrays.asList("foo", "bar"), actual
+    assertEquals(asList("foo", "bar"), actual
             .getIncludedTestMethods());
   }
 
@@ -388,7 +386,7 @@ public void testParsesExcludedClasspathElements()
     artifacts.add(dependency);
     when(this.project.getArtifacts()).thenReturn(artifacts);
     when(this.project.getTestClasspathElements()).thenReturn(
-        Arrays.asList("group" + sep + "artifact" + sep + "1.0.0" + sep
+        asList("group" + sep + "artifact" + sep + "1.0.0" + sep
             + "group-artifact-1.0.0.jar"));
 
     final ReportOptions actual = parseConfig("<classpathDependencyExcludes>"
@@ -470,6 +468,35 @@ public void testEvaluatesNormalPropertiesInArgLines() {
     assertThat(actual.getArgLine()).isEqualTo("fooValue barValue");
   }
 
+  public void testAddsModulesToMutationPathWhenCrossModule() {
+    MavenProject dependedOn = project("com.example", "foo");
+    MavenProject notDependedOn = project("com.example", "bar");
+
+    when(session.getProjects()).thenReturn(asList(dependedOn, notDependedOn));
+
+    Dependency dependency = new Dependency();
+    dependency.setGroupId("com.example");
+    dependency.setArtifactId("foo");
+    when(project.getDependencies()).thenReturn(asList(dependency));
+
+    final ReportOptions actual = parseConfig("<crossModule>true</crossModule>");
+
+    assertThat(actual.getCodePaths()).contains("foobuild");
+    assertThat(actual.getCodePaths()).doesNotContain("barbuild");
+  }
+
+  private static MavenProject project(String group, String artefact) {
+    MavenProject dependedOn = new MavenProject();
+    dependedOn.setGroupId(group);
+    dependedOn.setArtifactId(artefact);
+
+    Build build = new Build();
+    build.setOutputDirectory(artefact + "build");
+    dependedOn.setBuild(build);
+
+    return dependedOn;
+  }
+
   private ReportOptions parseConfig(final String xml) {
     try {
       final String pom = createPomWithConfiguration(xml);