This paper examines the nature and context of breaching (leaping from the water) and lobtailing (thrashing of flukes onto the water surface) in sperm whales (Physeter macrocephalus) using data principally collected off the Galápagos Islands. Animals generally breached on their sides at an angle of 30–50° to the water surface and with about 50–100% of their body showing at peak emergence. Breaches and lobtails were often found to occur in long sessions or "bouts" lasting up to several hours and at times containing over 250 individual activities. The rates of observing these activities did not vary seasonally, but breaching was seen more often in 1985 than in 1987, an El Niño year when the whales appeared to have reduced feeding success. Both breaching and lobtailing rates were highest in the late afternoon, although both activities occurred at all times of day and night. Bouts of breaches and lobtails were longer when several groups of sperm whales were together, and during long bouts, groups or small clusters of whales frequently merged or split up. Except for two breaches, all aerial activity was observed from groups of female and immature whales rather than from mature or maturing males on breeding or feeding grounds.