The Happiest Baby on the Block by Harvey Karp

Karp's "5 S's" method — swaddling, side/stomach position, shushing, swinging, and sucking — has saved the sanity of millions of parents dealing with inconsolable newborns. The core insight is that babies have a "fourth trimester" and need womb-like conditions to calm down. It sounds too simple to work. Then you try it at 3 AM and your screaming baby falls asleep in 90 seconds.