This thesis investigates the coastal morphology and processes of Rarotonga, Cook Islands. Field research was undertaken in Rarotonga, between January and April 1993. This investigation was conducted at differing spatial scales and levels of Intensity. In order to obtain a wide understanding of the coastal environment of Rarotonga, two phases of inter-related field research were conducted. The first phase circumnavigated the coast of Rarotonga, conducting general observations and measurements of .a series of beach parameters including slope, width and sediment characteristics, and lagoon parameters including water depth, width of the reef flat and sediment characteristics. These general observations led to the development of three classification systems for the coastal environment of Rarotonga that categorise different beaches based on the various coastal parameters observed. The second phase of field research was undertaken at two sites that exhibit different beach and lagoon morphologies. The characteristics of breaking waves, waves that have reformed on the reef flat and waves that break on the shore were observed. Recordings of water levels and current velocities were undertaken on the reef flat in an attempt to establish any relationships that exists between wave action on the reef crest and process characteristics on the reef flat. Results indicate that beach and lagoon morphology and sediment characteristics are spatially diverse around the coast of Rarotonga. Processes of water circulation within the lagoons are highly variable and complex due to the generation of 'alternative' current flows which interact with the dominant flows, causing irregularities in circulation. The alternative currents result from the interaction of a number of processes, primarily variations in lagoon geometry, wave and wind characteristics and orientation of reef structure. The nature and magnitude of coastal processes differ considerably around the island, due to variability in the modification of waves by the reef structure. Low energy processes experienced at the study areas are not the'· dominant processes of beach and lagoon development, instead more infrequent high energy events are thought to be responsible.