Throughout the period between 1790 and 1914 the governments of the Australian colonies asked their populations to suspend work and amusements and join in collective acts of prayer. Australia’s special days of prayer have much historical significance and deserve more scholarly attention. They had an enduring popularity, and they were rare moments when a multi-faith and multi-ethnic community joined together to worship for a common cause. This article builds on recent work on state prayers in Britain by considering what the colonial tradition of special worship can tell us about community attachments in nineteenth-century Australia. ‘Fast days’ and ‘days of thanksgiving’ had both an imperial and a regional character. A small number of the Australian days were for imperial events (notably wars and royal occasions) that were observed on an empire-wide scale. The great majority, such as the numerous days of fasting and humiliation that were called during periods of drought, were for regional happenings and were appointed by colonial authorities. The article argues that the different types of prayer day map on to the various ways that contemporaries envisaged ‘Greater Britain’ and the ‘British world’. Prayer days for royal events helped the empire’s inhabitants to regard themselves as imperial Britons. Meanwhile, days appointed locally by colonial governments point to the strength of regional attachments. Colonists developed a sense that providence treated them differently from British communities elsewhere, and this sense of ‘national providence’ could underpin a sense of colonial difference—even a colonial nationalism. Days of prayer suggested that Greater Britain was a composite of separate communities and nationalities, but the regional feelings they encouraged could still sit comfortably with attachments to an imperial community defined by commonalities of race, religion and interest.