Tagging introduction 

Low tech

The short history of tagging - A quick background to what MP3 and ID3 are.
ID3v2 made easy - A non-technical introduction to ID3v2.

Mid tech
ID3 made easy - A short description of ID3 (v1 and v1.1).
Lyrics3 made easy - A quick look at a tagging format for lyrics.
Lyrics3 v2.00 - A closer look to the latest Lyrics3 standard.
The private life of MP3 frames - How does the internal of an MP3 file look like.