diff --git a/lib/codegen/fromcto/java/javavisitor.js b/lib/codegen/fromcto/java/javavisitor.js
index 08160891..a3f296cf 100644
--- a/lib/codegen/fromcto/java/javavisitor.js
+++ b/lib/codegen/fromcto/java/javavisitor.js
@@ -288,7 +288,7 @@ class JavaVisitor {
                 break;
             default:
                 if (ModelUtil.isMap(field)) {
-                    const decl = field.getModelFile().getType(field.ast.type.name);
+                    const decl = field.getModelFile().getType(field.getType());
                     parameters.fileWriter.writeLine(1, `private Map<${this.toJavaType(decl.getKey().getType())}, ${this.toJavaType(decl.getValue().getType())}> ${field.getName()} = new HashMap<>();`);
                 } else {
                     parameters.fileWriter.writeLine(1, 'private ' + fieldType + ' ' + fieldName + ';' );
diff --git a/lib/codegen/fromcto/protobuf/protobufvisitor.js b/lib/codegen/fromcto/protobuf/protobufvisitor.js
index 24858134..9cde4e0a 100644
--- a/lib/codegen/fromcto/protobuf/protobufvisitor.js
+++ b/lib/codegen/fromcto/protobuf/protobufvisitor.js
@@ -57,12 +57,12 @@ class ProtobufVisitor {
 
     /**
      * Transform a Concerto primitive type into a Proto3 one.
-     * @param {Object} field - the Concerto primitive type
+     * @param {Object} type - the Concerto primitive type
      * @return {Object} the Proto3 primitive type
      * @public
      */
-    concertoToProto3PrimitiveType(field) {
-        switch (field.getType()) {
+    concertoToProto3PrimitiveType(type) {
+        switch (type) {
         case 'String':
             return 'string';
         case 'Double':
@@ -394,9 +394,23 @@ class ProtobufVisitor {
         debug('entering visitField', field.getName());
 
         const preposition = this.concertoToProto3FieldRule(field);
+
+        if (ModelUtil.isMap(field)) {
+            const mapDeclaration = field.getModelFile().getType(field.getType());
+            const keyType = mapDeclaration.getKey().getType();
+            const valueType = mapDeclaration.getValue().getType();
+
+            let key = ModelUtil.isPrimitiveType(keyType) ? this.concertoToProto3PrimitiveType(keyType) : keyType;
+            let value = ModelUtil.isPrimitiveType(valueType) ? this.concertoToProto3PrimitiveType(valueType) : valueType;
+
+            parameters.fileWriter.writeLine(0, `  ${preposition ? `${preposition} ` : ''}map<${key}, ${value}> ${mapDeclaration.getName()} = ${parameters.fieldIndex ?? '0'};`);
+
+            return;
+        }
+
         const type = field.isPrimitive()
             // Primitive Concerto types are mapped to specific Proto3 types.
-            ? this.concertoToProto3PrimitiveType(field)
+            ? this.concertoToProto3PrimitiveType(field.getType())
             // The rest are references to classes and enums.
             : this.concertoToProto3MessageOrEnumType(field);
         // Proto3 is not happy with the "$" sign, so we are replacing it with an "_".
diff --git a/test/codegen/__snapshots__/codegen.js.snap b/test/codegen/__snapshots__/codegen.js.snap
index 35c8d7ed..3a3846ab 100644
--- a/test/codegen/__snapshots__/codegen.js.snap
+++ b/test/codegen/__snapshots__/codegen.js.snap
@@ -3681,11 +3681,11 @@ import "google/protobuf/timestamp.proto";
 import "org.acme.hr.base.v.proto";
 
 message Company {
-  optional CompanyProperties companyProperties = 1;
-  optional EmployeeDirectory employeeDirectory = 2;
-  optional EmployeeProfiles employeeProfiles = 3;
-  optional EmployeeSocialSecurityNumbers employeeSocialSecurityNumbers = 4;
-  optional EmployeeTShirtSizes employeeTShirtSizes = 5;
+  optional map<string, string> CompanyProperties = 1;
+  optional map<SSN, Employee> EmployeeDirectory = 2;
+  optional map<string, Concept> EmployeeProfiles = 3;
+  optional map<string, SSN> EmployeeSocialSecurityNumbers = 4;
+  optional map<SSN, TShirtSizeType> EmployeeTShirtSizes = 5;
   Address headquarters = 6;
   string name = 7;
 }
@@ -3735,7 +3735,7 @@ message Employee {
   string lastName = 9;
   optional string manager = 10;
   optional string middleNames = 11;
-  NextOfKin nextOfKin = 12;
+  map<KinName, KinTelephone> NextOfKin = 12;
   sint64 numDependents = 13;
   Address officeAddress = 14;
   bool retired = 15;
@@ -3760,7 +3760,7 @@ message Contractor {
   string lastName = 7;
   optional string manager = 8;
   optional string middleNames = 9;
-  NextOfKin nextOfKin = 10;
+  map<KinName, KinTelephone> NextOfKin = 10;
   string ssn = 11;
 }
 
@@ -3776,7 +3776,7 @@ message Manager {
   string lastName = 9;
   optional string manager = 10;
   optional string middleNames = 11;
-  NextOfKin nextOfKin = 12;
+  map<KinName, KinTelephone> NextOfKin = 12;
   sint64 numDependents = 13;
   Address officeAddress = 14;
   repeated string reports = 15;
@@ -9314,11 +9314,11 @@ import "google/protobuf/timestamp.proto";
 import "org.acme.hr.base.v1_0_0.proto";
 
 message Company {
-  optional CompanyProperties companyProperties = 1;
-  optional EmployeeDirectory employeeDirectory = 2;
-  optional EmployeeProfiles employeeProfiles = 3;
-  optional EmployeeSocialSecurityNumbers employeeSocialSecurityNumbers = 4;
-  optional EmployeeTShirtSizes employeeTShirtSizes = 5;
+  optional map<string, string> CompanyProperties = 1;
+  optional map<SSN, Employee> EmployeeDirectory = 2;
+  optional map<string, Concept> EmployeeProfiles = 3;
+  optional map<string, SSN> EmployeeSocialSecurityNumbers = 4;
+  optional map<SSN, TShirtSizeType> EmployeeTShirtSizes = 5;
   Address headquarters = 6;
   string name = 7;
 }
@@ -9368,7 +9368,7 @@ message Employee {
   string lastName = 9;
   optional string manager = 10;
   optional string middleNames = 11;
-  NextOfKin nextOfKin = 12;
+  map<KinName, KinTelephone> NextOfKin = 12;
   sint64 numDependents = 13;
   Address officeAddress = 14;
   bool retired = 15;
@@ -9393,7 +9393,7 @@ message Contractor {
   string lastName = 7;
   optional string manager = 8;
   optional string middleNames = 9;
-  NextOfKin nextOfKin = 10;
+  map<KinName, KinTelephone> NextOfKin = 10;
   string ssn = 11;
 }
 
@@ -9409,7 +9409,7 @@ message Manager {
   string lastName = 9;
   optional string manager = 10;
   optional string middleNames = 11;
-  NextOfKin nextOfKin = 12;
+  map<KinName, KinTelephone> NextOfKin = 12;
   sint64 numDependents = 13;
   Address officeAddress = 14;
   repeated string reports = 15;
diff --git a/test/codegen/fromcto/protobuf/protobufvisitor.js b/test/codegen/fromcto/protobuf/protobufvisitor.js
index 6fe741f2..077956df 100644
--- a/test/codegen/fromcto/protobuf/protobufvisitor.js
+++ b/test/codegen/fromcto/protobuf/protobufvisitor.js
@@ -30,6 +30,7 @@ const ModelManager = require('@accordproject/concerto-core').ModelManager;
 const ModelLoader = require('@accordproject/concerto-core').ModelLoader;
 const AssetDeclaration = require('@accordproject/concerto-core').AssetDeclaration;
 const ClassDeclaration = require('@accordproject/concerto-core').ClassDeclaration;
+const MapDeclaration = require('@accordproject/concerto-core').MapDeclaration;
 const EnumDeclaration = require('@accordproject/concerto-core').EnumDeclaration;
 const EnumValueDeclaration = require('@accordproject/concerto-core').EnumValueDeclaration;
 const Field = require('@accordproject/concerto-core').Field;
@@ -37,6 +38,9 @@ const RelationshipDeclaration = require('@accordproject/concerto-core').Relation
 const TransactionDeclaration = require('@accordproject/concerto-core').TransactionDeclaration;
 const FileWriter = require('@accordproject/concerto-util').FileWriter;
 const { InMemoryWriter } = require('@accordproject/concerto-util');
+const ModelUtil = require('@accordproject/concerto-core').ModelUtil;
+let sandbox = sinon.createSandbox();
+
 
 describe('ProtobufVisitor', function () {
     let protobufVisitor;
@@ -277,6 +281,12 @@ describe('ProtobufVisitor', function () {
     });
 
     describe('visitField', () => {
+        before(() => {
+            sandbox.stub(ModelUtil, 'isMap').callsFake(() => {
+                return false;
+            });
+        });
+
         it('should return an object representing a Proto3 field coming from a Concerto String', () => {
             let param = {
                 fileWriter: mockFileWriter
@@ -396,10 +406,313 @@ describe('ProtobufVisitor', function () {
             param.fileWriter.writeLine.callCount.should.deep.equal(1);
             param.fileWriter.writeLine.getCall(0).args.should.deep.equal([0, '  repeated string Bob = 0;']);
         });
+
+        it('should return an object representing a Proto3 field that is a map <String, String>', () => {
+            let param = {
+                fileWriter: mockFileWriter
+            };
+
+            sandbox.restore();
+
+            sandbox.stub(ModelUtil, 'isMap').callsFake(() => {
+                return true;
+            });
+
+            const getType               = sinon.stub();
+            const mockMapDeclaration    = sinon.createStubInstance(MapDeclaration);
+            const mockField             = sinon.createStubInstance(Field);
+            const findStub              = sinon.stub();
+            const getKeyType            = sinon.stub();
+            const getValueType          = sinon.stub();
+
+            mockField.getModelFile.returns({ getType: getType });
+            getType.returns(mockMapDeclaration);
+            findStub.returns(mockMapDeclaration);
+            getKeyType.returns('String');
+            getValueType.returns('String');
+            mockMapDeclaration.getName.returns('map1');
+            mockMapDeclaration.isMapDeclaration.returns(true);
+            mockMapDeclaration.getKey.returns({ getType: getKeyType });
+            mockMapDeclaration.getValue.returns({ getType: getValueType });
+
+            protobufVisitor.visitField(mockField, param);
+            param.fileWriter.writeLine.callCount.should.deep.equal(1);
+            param.fileWriter.writeLine.getCall(0).args.should.deep.equal([0, '  map<string, string> map1 = 0;']);
+
+            sandbox.restore();
+        });
+
+        it('should return an object representing a Proto3 field that is a map <String, DateTime>', () => {
+            let param = {
+                fileWriter: mockFileWriter
+            };
+
+            sandbox.stub(ModelUtil, 'isMap').callsFake(() => {
+                return true;
+            });
+
+            const getType               = sinon.stub();
+            const mockMapDeclaration    = sinon.createStubInstance(MapDeclaration);
+            const mockField             = sinon.createStubInstance(Field);
+            const findStub              = sinon.stub();
+            const getKeyType            = sinon.stub();
+            const getValueType          = sinon.stub();
+
+            mockField.getModelFile.returns({ getType: getType });
+            getType.returns(mockMapDeclaration);
+            findStub.returns(mockMapDeclaration);
+            getKeyType.returns('String');
+            getValueType.returns('DateTime');
+            mockMapDeclaration.getName.returns('map1');
+            mockMapDeclaration.isMapDeclaration.returns(true);
+            mockMapDeclaration.getKey.returns({ getType: getKeyType });
+            mockMapDeclaration.getValue.returns({ getType: getValueType });
+
+            protobufVisitor.visitField(mockField, param);
+            param.fileWriter.writeLine.callCount.should.deep.equal(1);
+            param.fileWriter.writeLine.getCall(0).args.should.deep.equal([0, '  map<string, google.protobuf.Timestamp> map1 = 0;']);
+
+            sandbox.restore();
+        });
+
+        it('should return an object representing a Proto3 field that is a map <String, SSN>', () => {
+            let param = {
+                fileWriter: mockFileWriter
+            };
+
+            sandbox.stub(ModelUtil, 'isMap').callsFake(() => {
+                return true;
+            });
+
+            const getType               = sinon.stub();
+            const mockMapDeclaration    = sinon.createStubInstance(MapDeclaration);
+            const mockField             = sinon.createStubInstance(Field);
+            const findStub              = sinon.stub();
+            const getKeyType            = sinon.stub();
+            const getValueType          = sinon.stub();
+
+            mockField.getModelFile.returns({ getType: getType });
+            getType.returns(mockMapDeclaration);
+            findStub.returns(mockMapDeclaration);
+            getKeyType.returns('String');
+            getValueType.returns('SSN');
+            mockMapDeclaration.getName.returns('map1');
+            mockMapDeclaration.isMapDeclaration.returns(true);
+            mockMapDeclaration.getKey.returns({ getType: getKeyType });
+            mockMapDeclaration.getValue.returns({ getType: getValueType });
+
+            protobufVisitor.visitField(mockField, param);
+            param.fileWriter.writeLine.callCount.should.deep.equal(1);
+            param.fileWriter.writeLine.getCall(0).args.should.deep.equal([0, '  map<string, SSN> map1 = 0;']);
+
+            sandbox.restore();
+        });
+
+        it('should return an object representing a Proto3 field that is a map <String, Concept>', () => {
+            let param = {
+                fileWriter: mockFileWriter
+            };
+
+            sandbox.stub(ModelUtil, 'isMap').callsFake(() => {
+                return true;
+            });
+
+            const getType               = sinon.stub();
+            const mockMapDeclaration    = sinon.createStubInstance(MapDeclaration);
+            const mockField             = sinon.createStubInstance(Field);
+            const findStub              = sinon.stub();
+            const getKeyType            = sinon.stub();
+            const getValueType          = sinon.stub();
+
+            mockField.getModelFile.returns({ getType: getType });
+            getType.returns(mockMapDeclaration);
+            findStub.returns(mockMapDeclaration);
+            getKeyType.returns('String');
+            getValueType.returns('Concept');
+            mockMapDeclaration.getName.returns('map1');
+            mockMapDeclaration.isMapDeclaration.returns(true);
+            mockMapDeclaration.getKey.returns({ getType: getKeyType });
+            mockMapDeclaration.getValue.returns({ getType: getValueType });
+
+            protobufVisitor.visitField(mockField, param);
+            param.fileWriter.writeLine.callCount.should.deep.equal(1);
+            param.fileWriter.writeLine.getCall(0).args.should.deep.equal([0, '  map<string, Concept> map1 = 0;']);
+
+            sandbox.restore();
+        });
+
+        it('should return an object representing a Proto3 field that is a map <SSN, String>', () => {
+            let param = {
+                fileWriter: mockFileWriter
+            };
+
+            sandbox.stub(ModelUtil, 'isMap').callsFake(() => {
+                return true;
+            });
+
+            const getType               = sinon.stub();
+            const mockMapDeclaration    = sinon.createStubInstance(MapDeclaration);
+            const mockField             = sinon.createStubInstance(Field);
+            const findStub              = sinon.stub();
+            const getKeyType            = sinon.stub();
+            const getValueType          = sinon.stub();
+
+            mockField.getModelFile.returns({ getType: getType });
+            getType.returns(mockMapDeclaration);
+            findStub.returns(mockMapDeclaration);
+            getKeyType.returns('SSN');
+            getValueType.returns('String');
+            mockMapDeclaration.getName.returns('map1');
+            mockMapDeclaration.isMapDeclaration.returns(true);
+            mockMapDeclaration.getKey.returns({ getType: getKeyType });
+            mockMapDeclaration.getValue.returns({ getType: getValueType });
+
+            protobufVisitor.visitField(mockField, param);
+            param.fileWriter.writeLine.callCount.should.deep.equal(1);
+            param.fileWriter.writeLine.getCall(0).args.should.deep.equal([0, '  map<SSN, string> map1 = 0;']);
+
+            sandbox.restore();
+        });
+
+        it('should return an object representing a Proto3 field that is a map <SSN, Employee>', () => {
+            let param = {
+                fileWriter: mockFileWriter
+            };
+
+            sandbox.restore();
+
+            sandbox.stub(ModelUtil, 'isMap').callsFake(() => {
+                return true;
+            });
+
+            const getType               = sinon.stub();
+            const mockMapDeclaration    = sinon.createStubInstance(MapDeclaration);
+            const mockField             = sinon.createStubInstance(Field);
+            const findStub              = sinon.stub();
+            const getKeyType            = sinon.stub();
+            const getValueType          = sinon.stub();
+
+
+            mockField.getModelFile.returns({ getType: getType });
+            getType.returns(mockMapDeclaration);
+            findStub.returns(mockMapDeclaration);
+            getKeyType.returns('SSN');
+            getValueType.returns('Employee');
+            mockMapDeclaration.getName.returns('map1');
+            mockMapDeclaration.isMapDeclaration.returns(true);
+            mockMapDeclaration.getKey.returns({ getType: getKeyType });
+            mockMapDeclaration.getValue.returns({ getType: getValueType });
+
+            protobufVisitor.visitField(mockField, param);
+            param.fileWriter.writeLine.callCount.should.deep.equal(1);
+            param.fileWriter.writeLine.getCall(0).args.should.deep.equal([0, '  map<SSN, Employee> map1 = 0;']);
+
+            sandbox.restore();
+        });
+
+        it('should return an object representing a Proto3 field that is a map <String, Double>', () => {
+            let param = {
+                fileWriter: mockFileWriter
+            };
+
+            sandbox.restore();
+
+            sandbox.stub(ModelUtil, 'isMap').callsFake(() => {
+                return true;
+            });
+
+            const getType               = sinon.stub();
+            const mockMapDeclaration    = sinon.createStubInstance(MapDeclaration);
+            const mockField             = sinon.createStubInstance(Field);
+            const findStub              = sinon.stub();
+            const getKeyType            = sinon.stub();
+            const getValueType          = sinon.stub();
+
+            mockField.getModelFile.returns({ getType: getType });
+            getType.returns(mockMapDeclaration);
+            findStub.returns(mockMapDeclaration);
+            getKeyType.returns('String');
+            getValueType.returns('Double');
+            mockMapDeclaration.getName.returns('map1');
+            mockMapDeclaration.isMapDeclaration.returns(true);
+            mockMapDeclaration.getKey.returns({ getType: getKeyType });
+            mockMapDeclaration.getValue.returns({ getType: getValueType });
+
+            protobufVisitor.visitField(mockField, param);
+            param.fileWriter.writeLine.callCount.should.deep.equal(1);
+            param.fileWriter.writeLine.getCall(0).args.should.deep.equal([0, '  map<string, double> map1 = 0;']);
+        });
+
+        it('should return an object representing a Proto3 field that is a map <String, Integer>', () => {
+            let param = {
+                fileWriter: mockFileWriter
+            };
+
+            sandbox.restore();
+
+            sandbox.stub(ModelUtil, 'isMap').callsFake(() => {
+                return true;
+            });
+
+            const getType               = sinon.stub();
+            const mockMapDeclaration    = sinon.createStubInstance(MapDeclaration);
+            const mockField             = sinon.createStubInstance(Field);
+            const findStub              = sinon.stub();
+            const getKeyType            = sinon.stub();
+            const getValueType          = sinon.stub();
+
+            mockField.getModelFile.returns({ getType: getType });
+            getType.returns(mockMapDeclaration);
+            findStub.returns(mockMapDeclaration);
+            getKeyType.returns('String');
+            getValueType.returns('Integer');
+            mockMapDeclaration.getName.returns('map1');
+            mockMapDeclaration.isMapDeclaration.returns(true);
+            mockMapDeclaration.getKey.returns({ getType: getKeyType });
+            mockMapDeclaration.getValue.returns({ getType: getValueType });
+
+            protobufVisitor.visitField(mockField, param);
+            param.fileWriter.writeLine.callCount.should.deep.equal(1);
+            param.fileWriter.writeLine.getCall(0).args.should.deep.equal([0, '  map<string, sint64> map1 = 0;']);
+        });
+
+        it('should return an object representing a Proto3 field that is a map <String, Long>', () => {
+            let param = {
+                fileWriter: mockFileWriter
+            };
+
+            sandbox.restore();
+
+            sandbox.stub(ModelUtil, 'isMap').callsFake(() => {
+                return true;
+            });
+
+            const getType               = sinon.stub();
+            const mockMapDeclaration    = sinon.createStubInstance(MapDeclaration);
+            const mockField             = sinon.createStubInstance(Field);
+            const findStub              = sinon.stub();
+            const getKeyType            = sinon.stub();
+            const getValueType          = sinon.stub();
+
+            mockField.getModelFile.returns({ getType: getType });
+            getType.returns(mockMapDeclaration);
+            findStub.returns(mockMapDeclaration);
+            getKeyType.returns('String');
+            getValueType.returns('Long');
+            mockMapDeclaration.getName.returns('map1');
+            mockMapDeclaration.isMapDeclaration.returns(true);
+            mockMapDeclaration.getKey.returns({ getType: getKeyType });
+            mockMapDeclaration.getValue.returns({ getType: getValueType });
+
+            protobufVisitor.visitField(mockField, param);
+            param.fileWriter.writeLine.callCount.should.deep.equal(1);
+            param.fileWriter.writeLine.getCall(0).args.should.deep.equal([0, '  map<string, sint64> map1 = 0;']);
+        });
     });
 
     describe('visit CTO file', () => {
         it('should process an APAP protocol CTO file', async () => {
+            sandbox.restore();
             const modelManager = await ModelLoader.loadModelManager(
                 [path.resolve(__dirname, './data/apapProtocol.cto')]
             );
diff --git a/types/lib/codegen/fromcto/protobuf/protobufvisitor.d.ts b/types/lib/codegen/fromcto/protobuf/protobufvisitor.d.ts
index 44ebc773..b0afbff9 100644
--- a/types/lib/codegen/fromcto/protobuf/protobufvisitor.d.ts
+++ b/types/lib/codegen/fromcto/protobuf/protobufvisitor.d.ts
@@ -23,11 +23,11 @@ declare class ProtobufVisitor {
     public concertoToProto3FieldRule(field: any): any;
     /**
      * Transform a Concerto primitive type into a Proto3 one.
-     * @param {Object} field - the Concerto primitive type
+     * @param {Object} type - the Concerto primitive type
      * @return {Object} the Proto3 primitive type
      * @public
      */
-    public concertoToProto3PrimitiveType(field: any): any;
+    public concertoToProto3PrimitiveType(type: any): any;
     /**
      * Transform a Concerto class or enum type into a Proto3 message or enum one.
      * @param {Object} field - the Concerto class or enum type