A method and apparatus for encoding and decoding three-dimensional (3D) image data is provided. The method of encoding 3D image data uses a data unit that includes a header area and a data area. Type information which indicates a type of data included in the data area is included in the header area, includes: encoding reference view image data and additional view image data for providing a 3D image; generating a first data unit by adding to the reference view image data a header which includes first unit type information from among pieces of type information defined in a legacy device; and generates a second data unit by adding to the additional view image data a header which includes second unit type information from among pieces of type information not defined in the legacy device.