diff --git a/src/main/java/org/cyclonedx/model/License.java b/src/main/java/org/cyclonedx/model/License.java
index 3cdffd438..46dc30c73 100644
--- a/src/main/java/org/cyclonedx/model/License.java
+++ b/src/main/java/org/cyclonedx/model/License.java
@@ -18,6 +18,7 @@
  */
 package org.cyclonedx.model;
 
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
 import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
@@ -30,6 +31,7 @@
 import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlElementWrapper;
 import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;
 import org.cyclonedx.Version;
+import org.cyclonedx.model.license.Acknowledgement;
 import org.cyclonedx.util.deserializer.PropertiesDeserializer;
 
 @SuppressWarnings("unused")
@@ -51,7 +53,7 @@ public class License extends ExtensibleElement {
     @JacksonXmlProperty(isAttribute = true, localName = "acknowledgement")
     @JsonProperty("acknowledgement")
     @VersionFilter(Version.VERSION_16)
-    private String acknowledgement;
+    private Acknowledgement acknowledgement;
 
     @VersionFilter(Version.VERSION_15)
     private Licensing licensing;
@@ -120,6 +122,13 @@ public void setProperties(final List<Property> properties) {
         this.properties = properties;
     }
 
+    public void addProperty(Property property) {
+        if(this.properties == null) {
+            this.properties = new ArrayList<>();
+        }
+        this.properties.add(property);
+    }
+
     public AttachmentText getAttachmentText() {
         return attachmentText;
     }
@@ -128,11 +137,11 @@ public void setLicenseText(AttachmentText attachmentText) {
         this.attachmentText = attachmentText;
     }
 
-    public String getAcknowledgement() {
+    public Acknowledgement getAcknowledgement() {
         return acknowledgement;
     }
 
-    public void setAcknowledgement(final String acknowledgement) {
+    public void setAcknowledgement(final Acknowledgement acknowledgement) {
         this.acknowledgement = acknowledgement;
     }
 
diff --git a/src/main/java/org/cyclonedx/model/license/Acknowledgement.java b/src/main/java/org/cyclonedx/model/license/Acknowledgement.java
new file mode 100644
index 000000000..e317e0be9
--- /dev/null
+++ b/src/main/java/org/cyclonedx/model/license/Acknowledgement.java
@@ -0,0 +1,31 @@
+package org.cyclonedx.model.license;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import org.cyclonedx.model.ExternalReference.Type;
+
+public enum Acknowledgement
+{
+  @JsonProperty("declared")
+  DECLARED("declared"),
+  @JsonProperty("concluded")
+  CONCLUDED("concluded");
+
+  private final String name;
+
+  public String getValue() {
+    return this.name;
+  }
+
+  Acknowledgement(String name) {
+    this.name = name;
+  }
+
+  public static Acknowledgement fromString(String text) {
+    for (Acknowledgement t : Acknowledgement.values()) {
+      if (t.name.equals(text)) {
+        return t;
+      }
+    }
+    return null;
+  }
+}
diff --git a/src/main/java/org/cyclonedx/model/license/Expression.java b/src/main/java/org/cyclonedx/model/license/Expression.java
index 2a71aaba1..5ae298512 100644
--- a/src/main/java/org/cyclonedx/model/license/Expression.java
+++ b/src/main/java/org/cyclonedx/model/license/Expression.java
@@ -27,7 +27,7 @@ public class Expression
   @JacksonXmlProperty(isAttribute = true, localName = "acknowledgement")
   @JsonProperty("acknowledgement")
   @VersionFilter(Version.VERSION_16)
-  private String acknowledgement;
+  private Acknowledgement acknowledgement;
 
   @JacksonXmlText
   @JsonProperty("expression")
@@ -49,11 +49,11 @@ public void setBomRef(final String bomRef) {
     this.bomRef = bomRef;
   }
 
-  public String getAcknowledgement() {
+  public Acknowledgement getAcknowledgement() {
     return acknowledgement;
   }
 
-  public void setAcknowledgement(final String acknowledgement) {
+  public void setAcknowledgement(final Acknowledgement acknowledgement) {
     this.acknowledgement = acknowledgement;
   }
 
diff --git a/src/main/java/org/cyclonedx/util/deserializer/ExpressionDeserializer.java b/src/main/java/org/cyclonedx/util/deserializer/ExpressionDeserializer.java
index 3588b4ae0..40010e43e 100644
--- a/src/main/java/org/cyclonedx/util/deserializer/ExpressionDeserializer.java
+++ b/src/main/java/org/cyclonedx/util/deserializer/ExpressionDeserializer.java
@@ -24,6 +24,7 @@
 import com.fasterxml.jackson.databind.DeserializationContext;
 import com.fasterxml.jackson.databind.JsonDeserializer;
 import com.fasterxml.jackson.databind.JsonNode;
+import org.cyclonedx.model.license.Acknowledgement;
 import org.cyclonedx.model.license.Expression;
 
 public class ExpressionDeserializer
@@ -53,7 +54,7 @@ private Expression parseExpressionNode(JsonNode node) {
     }
 
     if (node.has("acknowledgement")) {
-      expression.setAcknowledgement(node.get("acknowledgement").asText());
+      expression.setAcknowledgement(Acknowledgement.fromString(node.get("acknowledgement").asText()));
     }
 
     JsonNode textNode = node.get("expression");
diff --git a/src/main/java/org/cyclonedx/util/serializer/LicenseChoiceSerializer.java b/src/main/java/org/cyclonedx/util/serializer/LicenseChoiceSerializer.java
index dc3e8797b..5438d9110 100644
--- a/src/main/java/org/cyclonedx/util/serializer/LicenseChoiceSerializer.java
+++ b/src/main/java/org/cyclonedx/util/serializer/LicenseChoiceSerializer.java
@@ -30,6 +30,7 @@
 import org.cyclonedx.model.License;
 import org.cyclonedx.model.LicenseChoice;
 import org.cyclonedx.model.Property;
+import org.cyclonedx.model.license.Acknowledgement;
 import org.cyclonedx.model.license.Expression;
 
 import static org.cyclonedx.util.serializer.SerializerUtils.shouldSerializeField;
@@ -129,7 +130,7 @@ else if (lc.getExpression() != null) {
   private void serializeXmlAttributes(
       final ToXmlGenerator toXmlGenerator,
       final String bomRef,
-      final String acknowledgement,
+      final Acknowledgement acknowledgement,
       final Object object) throws IOException
   {
     toXmlGenerator.writeStartObject();
@@ -140,10 +141,10 @@ private void serializeXmlAttributes(
       toXmlGenerator.writeString(bomRef);
       toXmlGenerator.setNextIsAttribute(false);
     }
-    if (StringUtils.isNotBlank(acknowledgement) && shouldSerializeField(object, version, "acknowledgement")) {
+    if (acknowledgement != null && shouldSerializeField(object, version, "acknowledgement")) {
       toXmlGenerator.setNextIsAttribute(true);
       toXmlGenerator.writeFieldName("acknowledgement");
-      toXmlGenerator.writeString(acknowledgement);
+      toXmlGenerator.writeString(acknowledgement.getValue());
       toXmlGenerator.setNextIsAttribute(false);
     }
   }
@@ -197,9 +198,8 @@ private void serializeExpressionToJson(final LicenseChoice licenseChoice, final
     gen.writeStartArray();
     gen.writeStartObject();
     gen.writeStringField("expression", expression.getValue());
-    if (StringUtils.isNotBlank(expression.getAcknowledgement()) &&
-        shouldSerializeField(expression, version, "acknowledgement")) {
-      gen.writeStringField("acknowledgement", expression.getAcknowledgement());
+    if (expression.getAcknowledgement() != null && shouldSerializeField(expression, version, "acknowledgement")) {
+      gen.writeStringField("acknowledgement", expression.getAcknowledgement().getValue());
     }
     if (StringUtils.isNotBlank(expression.getBomRef()) && shouldSerializeField(expression, version, "bomRef")) {
       gen.writeStringField("bom-ref", expression.getBomRef());
diff --git a/src/test/java/org/cyclonedx/parsers/AbstractParserTest.java b/src/test/java/org/cyclonedx/parsers/AbstractParserTest.java
index 6f62acf6b..aa8a2dca5 100644
--- a/src/test/java/org/cyclonedx/parsers/AbstractParserTest.java
+++ b/src/test/java/org/cyclonedx/parsers/AbstractParserTest.java
@@ -70,6 +70,7 @@
 import org.cyclonedx.model.formulation.trigger.Trigger;
 import org.cyclonedx.model.formulation.workspace.Volume;
 import org.cyclonedx.model.formulation.workspace.Workspace;
+import org.cyclonedx.model.license.Acknowledgement;
 import org.cyclonedx.model.vulnerability.Vulnerability;
 import org.cyclonedx.model.vulnerability.Vulnerability.Analysis.Justification;
 import org.cyclonedx.model.vulnerability.Vulnerability.Analysis.State;
@@ -1010,7 +1011,7 @@ void assertAck(Bom bom) {
     License license = lc.getLicenses().get(0);
     assertEquals("Apache-2.0", license.getId());
     assertEquals("my-license", license.getBomRef());
-    assertEquals("declared", license.getAcknowledgement());
+    assertEquals(Acknowledgement.DECLARED, license.getAcknowledgement());
   }
 
   Bom getXmlBom(String filename) throws ParseException, IOException {
diff --git a/src/test/java/org/cyclonedx/parsers/JsonParserTest.java b/src/test/java/org/cyclonedx/parsers/JsonParserTest.java
index 1cdccb4db..b534aa211 100644
--- a/src/test/java/org/cyclonedx/parsers/JsonParserTest.java
+++ b/src/test/java/org/cyclonedx/parsers/JsonParserTest.java
@@ -59,6 +59,7 @@
 import org.cyclonedx.model.definition.Level;
 import org.cyclonedx.model.definition.Requirement;
 import org.cyclonedx.model.definition.Standard;
+import org.cyclonedx.model.license.Acknowledgement;
 import org.cyclonedx.model.license.Expression;
 import org.junit.jupiter.api.Test;
 import java.io.File;
@@ -281,7 +282,7 @@ public void schema16_license_id_acknowledgement() throws Exception {
         License license = lc.getLicenses().get(0);
         assertEquals("Apache-2.0", license.getId());
         assertEquals("my-license", license.getBomRef());
-        assertEquals("declared", license.getAcknowledgement());
+        assertEquals(Acknowledgement.DECLARED, license.getAcknowledgement());
     }
 
     @Test
@@ -295,7 +296,7 @@ public void schema16_license_expression_acknowledgement() throws Exception {
         Expression expression = lc.getExpression();
         assertEquals("EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0", expression.getValue());
         assertEquals("my-license", expression.getBomRef());
-        assertEquals("declared", expression.getAcknowledgement());
+        assertEquals(Acknowledgement.DECLARED, expression.getAcknowledgement());
     }
 
     @Test
diff --git a/src/test/java/org/cyclonedx/parsers/XmlParserTest.java b/src/test/java/org/cyclonedx/parsers/XmlParserTest.java
index 997813e59..6e79b4f94 100644
--- a/src/test/java/org/cyclonedx/parsers/XmlParserTest.java
+++ b/src/test/java/org/cyclonedx/parsers/XmlParserTest.java
@@ -60,6 +60,7 @@
 import org.cyclonedx.model.definition.Level;
 import org.cyclonedx.model.definition.Requirement;
 import org.cyclonedx.model.definition.Standard;
+import org.cyclonedx.model.license.Acknowledgement;
 import org.cyclonedx.model.license.Expression;
 import org.junit.jupiter.api.Test;
 import java.io.File;
@@ -440,7 +441,7 @@ public void schema16_license_expression_acknowledgement() throws Exception {
         Expression expression = lc.getExpression();
         assertEquals("EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0", expression.getValue());
         assertEquals("my-license", expression.getBomRef());
-        assertEquals("declared", expression.getAcknowledgement());
+        assertEquals(Acknowledgement.DECLARED, expression.getAcknowledgement());
     }
 
     @Test