There are many good books on PostScript language programming. Descriptions of all known books are listed below. A listing of publisher information follows.
The most commonly known books are the ``blue book'', ``big red book'', and ``green book'' from Adobe, to be read in that order. They are nicknamed according for their jacket colors.
Other books recommended to me include Thinking in PostScript, which allows its examples to be freely distributed, and PostScript by Example.