Introduction to TypeSelectors TypeSelectors are what the MessageSerializer uses to determine what TypeSerializer class should be used to process a property on your class. When the MessageSerializer is processing a class to determine how it should be handled, it will go through each property that needs to be serialized and check the TypeSelectors that have been configured to determine which TypeSerializer should be used for the property. This is done by looping through the list of TypeSelectors that have been specified in the SerializationDefaults that are being used by the Serializer while processing the class. All TypeSelectors inherit from ITypeSelector which only requires implementing one function: Type CheckType(MessageSerializedPropertyInfo propertyInfo) The Type that is returned is of type TypeSerializerBase<T> where T is the PropertyType of the property that the TypeSerializer is being applied to. The exception is the case where the property is a List<SomeType>. In that case T will be SomeType instead. The TypeSelectors are processed in order until one returns a Type other than null. This can be important as for certain types you may need to make sure that the order of TypeSelectors will produce the desired result. See the note on TypeSelectorNumericBcd in the list of default TypeSelectors below. By default the SerializationDefaults class uses the following TypeSelectors (and in this order) TypeSelectorSpecifiedClass TypeSelectorSerializable TypeSelectorNumericBcd TypeSelectorEnum TypeSelectorNumeric TypeSelectorString TypeSelectorDateTime TypeSelectorByteArray See TypeSelectorUserDefined for information on how to make your own TypeSelectors.