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Echinoderms play a key role in structuring many marine ecosystems and are notorious for large population density variations in so‐called “outbreak” or “dieoff” events. In a review of this phenomenon, we assess the causal factors and ecological and evolutionary consequences. We identified 28 species (6 Asteroidea, 8 Echinoidea, 10 Holothuroidea, 4 Ophiuroidea) that exhibit large (more than two population doublings or halvings) population density changes. Three generalized patterns were identified and named for exemplary species: (1) rapid decreases followed by no or slow recovery (Diadema–Paracentrotus Model), (2), rapid increase and apparent stability at a new population density (Amperima–Amphiura Model), and (3) population density fluctuations (Acanthaster–Asterias Model). Echinoderms identified were distributed from the shallow intertidal to the deep sea, and from tropical to temperate regions. In …