The Book of the Die was written by George Cockcroft under the pen name Luke Rhinehart. It is mentioned as a fictional book in The Dice Man, Adventures of Wim, and The Search for the Dice Man, and he chose the year 2000 to make it a reality.

Warning: Wikipedia contains spoilers

The book is a collection of thoughts and ideas about dicing - its purpose, the meaning of life, and so forth - much in the style that might be expected from George Cockcroft's previous work. Interspersed with this are frequent parables, poems, stories. Some are from his earlier books, some from the new ones, some stolen and rewritten from various well-known sayings and writings, some from his followers (both real and imaginary), and some which purport to be from his own life.

The whole thing is broken into 21 chapters, plus an introduction and explanation of the whole thing. The idea is meant to be that you roll two dice to decide which chapter to read, or look for answers in, or perhaps flick through to pick one which seems appropriate, or maybe read in order like any other book. As long as people are aware of their options, eh?

Also, roughly at the end of each chapter are six dice options, with the standard instructions:

"Read the options, throw out one or two (or all six) and replace them, then roll a dice and do as suggested."

The dice options, and the book in general, aim to be intriguing and thought-provoking. It's in some sense a book with all the answers - written by someone who has thought about such things for most of his life. Yet it's also a book of no answers, as George Cockcroft consistently tries to ensure that the reader is aware that the book is just another illusion. "Dice living is a load of shit", he says at one point. Naturally it contains lots of amusing or absurd sections, as if to counter-point the occasional more serious sections.

The book was published under two different ISBNs: