The John Lennon encyclopedia, a book literally as thick as a brick, has probably everything a Lennon or Beatle fan will ever want to know about John Lennon. Within its 1002 pages you'll find information about John's life (childhood, Beatlehood & solo), origins of songs, the books he wrote in the early 1960s, origins of films he worked on with Yoko, relatives, friends, his children, celebrity accquaintences, TV appearances, autobiographies written about John, songs written about John, short stories about John, even messages that psychics claim to have come from John beyond the grave. Yep, absolutely everything about John there was up to the point of publication. The only thing I couldn't find was the origins of John's glasses!
Like the title suggests, the book is written like an encyclopedia. Facts about John have been given a title ("Drugs", "Epstein, Brian", "Mind Games", etc), and arranged in alphabetical order. This makes it very easy to find exactly what you want to know, as well as easy to read. You can dip into it and read as much or as little as you like. It's a good bedtime read for Beatlemaniacs like myself, and makes quite a hefty coffee table book.
This isn't a cash in by some puffed-up biased journalist, like a lot of Lennon nonfiction. This is Bill Harry, a man who not only went to the same art school as John, but was a good friend of his. Bill Harry as accurate and as thorough as he can be, and modest. If you look up "Bill Harry" in the encyclopedia, you won't find it, and when he is mentioned in the various entries about his art college years, Bill Harry talks about himself in the objective third person. Superstar biographies could learn a lot from this one.
An interesting read for the hardcore Beatle fan, and the trivia buff. A casual fan might want to start with the "The Beatles Anthology" instead, as that's written in order, and you'll have a place to start rather than being thrown into John's world. However, if you only want one Lennon nonfiction, this is the one to get.