The Great Barrier Reef, the world’s longest barrier reef, extends for 2000 km along the northeast coast of Australia. It is a complex feature, with outer ribbon reefs and inner platform and patch reefs of widely differing forms. Most previous work has concentrated in the extreme south (at Heron and One Tree Islands) or in the central sector (at Low Isles). The 1973 Expedition worked in the northern sector, from Cairns to the latitude of Cape Grafton (11° 30' S). The main aim of the Expedition was to elucidate the recent history of the reefs, especially in response to Holocene sea level change. Evidence was sought from shallow coring, geophysical surveys, studies of reef and inter-reef sediments, observations on modern reef communities, and the analysis of the geology and geomorphology of reef islands. The work of the field parties in each of these areas is briefly reviewed and related to the questions to be discussed in the following papers.