Over the last few decades, the use of space-borne radar altimetry has dramatically improved our knowledge and understanding of the oceans. During this same period, sea-level observation with tide gauges has also undergone spectacular changes, both from a technological point of view and in the applicative fields. This article gives a brief history of tidal observation and then explains how this discipline is closely linked both to geodesy and to oceanography. The renewed interest in tide gauges is illustrated using three case studies; these reflect how the discipline is complementary to space geodesy.