The Galaxy Guides are a series of source books for the original West End Star Wars RPG. The first 6 guides (numbers 1 till 6) were published between 1989 and 1990 to be used with the 1st edition.
The remaining 6 galaxy guides (numbers 7 till 12), published between 1993 and 1995, were published specifically for the 2nd edition Star Wars RPG which was released in 1992.
The original 6 galaxy guides were then updated for the 2nd edition as well, and were re-released with new covers, content and with the subtitle "Revised and Expanded for 2nd edition". This was between 1994 and 1995.
Each book deals with a specific part of the Star Wars universe, and the books are occasionally "narrated" by a fictional character, for example a historian who lectures about the battles of the Rebellion or a medical doctor's notes about alien races.