During 1961 to 1963 regular plankton tows were taken from Wellington Harbour. These plankton samples were analysed, the macroplankton fauna identified, and the abundance of each species recorded. Class Crustacea was made the subject of special study and identified larva illustrated. A plankton calendar of the dominant macro-plankton species was prepared and the characteristics of the plankton in each month described. Irregular variations are discussed. Surface water temperature variation was found to influence the abundance of numerically dominant species. Ecological factors determining the nature of the harbour population are discussed. The zooplankton of Wellington Harbour is compared with that of coastal New South Wales, Australia.