A knowledge of the key water masses and currents that affect New Zealand is invaluable to understanding near-shore and coastal processes, and the chemistry and biology of oceanic and coastal waters. This chapter introduces ocean circulation around New Zealand and discusses features and processes that are relevant to a broad understanding of the ocean and its impact on New Zealand. There is a brief introduction to the driving forces of oceanic circulation, followed by a short review of the geology and bathymetry of New Zealand waters. A synopsis of Antarctic and Pacific Ocean circulation patterns that affect the New Zealand ocean environment is discussed before the general and localised circulation is presented in some detail, with special attention given to unique features of New Zealand's ocean environment. The relevance of oceanic circulation to sedimentary processes, biological processes and ecosystem function (including fisheries) is discussed. Finally, the ability to detect spatial and temporal changes in ocean processes is reviewed in the context of climate change issues.