Illustrated 1972 guide by Alex Comfort which presents heterosexual intercourse as a series of courses in a meal (appetizer, entree, desert, etc). There's now a New Joy of Sex, and spinoffs like The Joy of Gay Sex.
Comfort's book is regarded as playing an important role in demystifying areas of sex, such as cunnilingus, masturbation, or anal sex. The tone of the book is non-judgemental and encourages a non male-centric view.
The illustrations of the orginal edition now look completely hilarious -- they're pencil drawings of long-haired hippy types engaged in some of the various activities and positions described in the book...
For the cookbook-imparied, the title is an allusion to The Joy of Cooking.