Detailed daily timetables of embryonic development of marsupials are rare and are confined to the Virginia and grey opossum (13.5 days), stripe-faced dunnart (10.7 days), agile antechinus (27 days). Less detailed timetables for other species are available. Many marsupial developmental timetables are characterised by developmental arrests during cleavage and the unilaminar blastocyst stages and these are used in reproductive strategies to ensure breeding success. This timetable of the brushtail possum was based on 183 specimens, of which 80 were timed from a plug, sperm in the urine or an observed mating (time 0) and the residue were wild-caught. Captive colony animals were monitored during oestrus and for several days around the expected day of birth. Samples were collected on each day, measured and photographed. Samples from wild-caught females were fitted into the timed samples. The gestation period pc was 15.5 days (range 15- 17 days) in captive colonies and showed evidence that oestrus could be extended for up to a couple of days but was mostly less than a day, several periods where maternal/conceptus interactions apparently occurred and no arrests during cleavage or unilaminar blastocyst stages. The direct development shown by the common brushtail possum, the marked synchrony of breeding in the autumn in NZ and the few developmental failures so that about 80% of females breed successfully in the wild suggest that the reproductive strategy used by the brushtail possum is to breed at the time of the year when survival of young is enhanced.