The MPEG-2 Standard is defined in ISO-13818, which is comprised of the following documents (some of them are also published by ITU):
- ISO-13818-2 aka ITU-T H.262
- Conformance testing (read if you want to write a multiplexer or an encoder)
- DSM-CC (Digital Storage Media Command and Control, used to transmit MHP applications and other data
- Advanced Audio Coding (AAC)
For a full list of the MPEG-2 standard's documents, see the ISO website.
In addition, given that the MPEG-2 Standard is a superset of the MPEG-1 Standard, you will find that it will, in places, refer to the older MPEG-1 standards documents (especially in the case of audio coding), so you may wish to read ISO-11172 as well.