First serialized in Collier's Magazine in 1954 then published as The Body Snatchers in 1955 and renamed after 1956 to match the film starring Kevin McCarthy. The 1978 "revised and updated" edition includes contemporary (if superfluous) references to President Carter and Watergate. It's the story of a doctor and his friends who discover that the inhabitants of their small California town are being replaced by aliens grown from seed pods that drifted to Earth from outer space. SF/horror hybrid, split roughly down the middle, with most of the really good stuff in the atmospheric first half. That's the half that makes this book a horror classic, with likable characters in chilling, suspenseful circumstances. To date, the book has been adapted to film four times, beginning with Don Siegel's version in 1956.
"The Body Snatchers," as serialized in Collier's (Nov. 26, Dec. 10, and Dec. 24, 1954), is worth reading in its own right. It's shorter, tighter, and features two significant differences from the novel. The first improves a decision the characters make at the halfway point, which leads directly to the second, an ending that is at once more formulaic than that of the novel yet also more believable. (Neither, however, explains the extra length of the novel, which is a result not of any new plot material really but simply of expansions and asides to existing ideas that are sometimes interesting in their own right, but not always particularly germane.)