Alcoholics Anonymous (or the 'Big Book' as it is commonly called) was first published in 1939 and was subtitled The Story of How Many Thousands of Men and Women Have Recovered from Alcoholism. It is the first text written about the experiences of the founders of the A.A. movement. It tells the story of Bill W., one of the co-founders of A.A. and how the program worked in the early days of the movement. It is full of much timeless and practical wisdom and is the first standard (and some would say the only standard) text of A.A. and, subsequently, of 12 step programs.
A more recent version of the Big Book can also be found online at the A.A. website. The newer versions differ mostly in the stories that are collected at the end of the book about people who have recovered using the 12 step approach.