Summary. 1 In the Cape the Redwinged Starling population consists of two parts: resident pairs and roving flocks. Pairs are territorial, usually roosting all year at the nest. Widowed males or females do not flock again, but quickly acquire new mates, in or out of the breeding season. 2 Flocks are probably composed mainly of juveniles, but with some sexually mature birds; incipient pairs may form in flocks. Flock movements, apparently related to changing food supplies, differ between areas but are broadly the same in any one area from year to year. They are conspicuous on the breeding grounds in the early breeding season. 3 Calls and territorial behaviour are described. Mirror experiments show that postures associated with preening have acquired significance as warning signals. The small territory (±2000 sq. yds.) is not used for feeding except incidentally. It is successfully defended against strange pairs, but not against flocks, which ignore pairs except during copulation. Other creatures (human beings, dogs, etc.) are boldly attacked near the nest, mainly during breeding but also at other times. 4 One method of pair-formation is described, but other methods must exist. 5 The male courts the female with food. The typical ceremony or parts of it may emerge in overt behaviour at inappropriate times. 6 Nest-site and building are described. 7 Two clutches are laid, normally in October and December; c/3 is usual, c/2 and c/4 fairly frequent. Eggs are laid on succeeding or alternate days. 8 Only the hen incubates and she starts sitting steadily before or with clutch completion. The apparent incubation period of earlier eggs may equal, or be up to 2 days longer or shorter than, that of the last egg. Periods for 14 clutches varied from 12½ to 23 days, average 16. In the same nests, fledging periods varied from 22 to 28 days, average 26. Thus the range of individual variation is 66% of the mean in incubation periods against 21% in fledging periods. 9 Hatching, brooding and development of the young are described. Observation and experiment showed that auditory stimuli release the gaping response in blind and also older nestlings. Behaviour at fledging is described, including an abnormal instance when the young were violently ejected by the male. 10 Breeding success is discussed and data supplied on food.