(FORTUNE Magazine) – What is it with all this dummy business? While Hollywood churns out the like of Forrest Gump and Dumb and Dumber, bookstores are brimming with paeans to simple-mindedness. In fact, books for dummies and idiots have become hot and hotter, thanks to clever publishers capitalizing on this new, dare we say lamebrained, trend.

Mutual Funds for Dummies, released in March, is the most recent in a series of about 150 Dummies titles published by IDG Books Worldwide, based in Foster City, California. The books offer simplified, alternative instruction to replace unintelligible owner's manuals and how-to guides. Over 15 million Dummies books have been sold, generating some $240 million in sales. On tap: Parenting for Dummies.

Dummies competitor Indianapolis-based Macmillan Publishing, through its Alpha Books division, offers The Complete Idiot's Guides, which are pitched by John Ratzenberger, who played Cliff, the major bonehead mailman in the TV series Cheers. Idiot's have sold about two million copies.

Gene Grossman, chairman of Anspach Grossman Portugal, a New York City brand consulting firm, explains why playing the dumb card seems to work. "Maybe people like getting talked down to a little bit. The implication is, 'it's gotta be simple because I'm a dummy and it's made for me.' "

- Suzanne Barlyn