Ebb and Flow: Tides and Life on Our Once and Future Planet is well titled. It tells the story of tides, why they matter, what causes them, and how they have changed over time. The author, Tom Koppel, is not an analyst or theoretician of tides but a man of inquisitive mind and substantial beachcombing and sailing experience. He tells his stories in an engaging style, be they of gathering clams on tidal flats or harrowing escapes from tidal races. They are woven into a well-paced and thoughtful narrative, never straying far from the tidal theme.