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Abstract: Moult is a vital avian process because it allows the renewal of the worn plumage in an organised way. Moult has a circannual periodicity and tends to differ between the first annual cycle (post-juvenile moult) and subsequent ones (post-breeding moult) of passerines, a fact that can be used to determine the age of individuals. We estimated wing-feather and rectrix moult-extent for 17 New Zealand passerines (excluding introduced species), classified each bird according to eight moult patterns, and computed frequency of wing-feather and rectrix replacement. We combined post-juvenile moult information with that of maturation of feathered and unfeathered characters to provide guidelines for age determination. Our results cover an important gap in the knowledge of the natural history of New Zealand passerines, generate reliable age determination criteria, and thus providing essential information for future conservation actions (including translocations) and to test hypotheses on the ecology and evolution of avian moult in the Australasian region.