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The breeding biology of kakapo (Strigops habroptilus) was investigated on offshore island refuges between 1990 and 2002. Male kakapo typically attended their display territories between October to April, with the primary courtship display, “booming”, usually beginning in January and ending in March. Mating was recorded from late December to March, with the median mating date falling in late January. Eggs were laid from early January to late March, with median dates of 24 January on Little Barrier Island and 7 February on Codfish and Pearl Islands. Females typically occupied a nest site eight days after their last mating (n = 44) and laid their first egg two days later (n = 40). Subsequent eggs were laid at three day intervals (n = 41). The mean and modal clutch sizes were 2.53 and 3 respectively, (range = 1 – 4, n = 54). Mean mass of fresh eggs was 40.53g (n = 122). Incubation began immediately after the first egg had been laid and the average incubation period was 30 days (n = 28). Mean nestling and fledgling periods were 72.4 (n = 27) and 246 days (n = 25) respectively. Male chicks began to grow more rapidly than females approximately one third through the nestling period. The mean fledging weights of 14 male and 14 female chicks were 1.93 and 1.72 kg respectively. Male kakapo are capable of mating at five years of age. Three known-age females first nested at 9, 10 and 11 years of age, respectively. Comparison with close relatives suggests that some aspects of kakapo breeding biology are evolutionarily conservative.