This thesis is in two parts. The first consists of 7 chapters made up of a short introduction and 6 papers either published, in the press, or in preparation, (Warham, 1963; 1971c; 1972; in press a. and b; and ms.) dealing with the biology of the individual species. The second part is a general review and discussion of particular aspects of the biology of these penguins based partly on the data given in the species accounts and partly on additional material. The objectives of the study were to uncover details of the main events during the breeding and moulting cycles of the various species of Eudyptes or crested penguins, and to describe their behaviour patterns. Most of these birds nest at great distance from centres of civilisation and consequently the work involved organising and undertaking visits to remote islands. These included Antipodes Island (6 weeks in 1969); Campbell Island (3 weeks in 1969); Macquarie Island (15 months in 1959 – 1961); and Snares Islands (3 to 6 weeks in 1967, 1968 and 1969). Field assistants collected additional data at Snares Island in 1969, 1970 and 1971. Partly because of the remoteness of the breeding places and the different times spent there, the amount and kind of data collected has varied from species to species. Thus while the information for E. chrysocome was based on daily observations over two breeding seasons, that for E. sclateri was mostly gained during only 6 weeks study at the nesting places. Similarly work on E. pachyrhynchus was undertaken over 6 seasons but, although the birds were observed at intervals from their arrival to their departure after the moult, observations could never be sustained for long periods. On the other hand, the parallel study of E. stratus was done over 5 seasons but with sustained observations only during the 4 months between chick raising and the annual moult. At the time of writing it has still not been possible to observe these birds from their arrival to the time of hatching of their eggs. This will be rectified in the 1972/73 breeding season. Not withstanding such logistic problems, these crested penguins have proved rewarding subjects and despite the uneven coverage, the general outlines of their breeding systems have been established and the main behavioural repertoire, hitherto mostly unrecorded, and has been set down. The new information contained in the thesis is too varied and numerous to list in detail. Before this study there had been no accurate and complete accounts of the annual cycles of and behaviour of any member of the genus. The present work will, it is hoped, go some way towards rectifying the lack of ecological information regarding New Zealand and Australian penguins about which Stonehouse (1967; p. 32) laid particular stress.