The Library of America (loa.org) decided it was time to honor Philip K. Dick and published four of his most famous novels in one volume. Good choice, since Dick's novels are in general quite short and publishing only one would have left the reader dissatisfied, given the tomes that are usually produced in the series.
The 60es were a crazy time by anyone's reckoning, at least in the United States (in Europe, the 70es would assume the same significance). Philip Dick, who was genuinely mentally troubled, works well as a paragon of the time – Dick and the Sixties, a match made in heaven.
The four novels in question are The Man in the High Castle, The Three Stigmata of Palmer Eldritch, Do Androids Dream of Electric Sheep, and Ubik. They have some themes in common, yet they show a visible evolution in the writing and thinking of the author.