Galley Reach, an estuary on the south coast of Papua New Guinea, is surrounded by some 14 000 ha of mangrove vegetation. Four main types of mangrove are mapped from airphotos and their species composition and ecology are described and discussed from ground observations. Soil water salinity ranged widely from less than 1‰ in the mangrove transitional to freshwater swamp vegetation to 55‰ in a bare saltflat. At the surface the salinity of open water ranged from around 9‰ in tidal creeks to between 1 and 3‰ near river mouths around low tide, but it increased markedly with depth to 20–26‰ below 4 m. The main mangrove species tend to grow in zones similar to those described from Malaysia and Australia. Regeneration is sparse under a closed forest canopy, but is usually prolific in gaps. For the main type, Rhizophora spp.- Bruguiera gymnorrhiza forest, the average basal area from 7 10×50 m sample plots was 30 m 2/ha. If this forest were to be regenerated naturally following exploitation, the main management problem is likely to be competition by Acrostichum and undesirable species of Bruguiera. The unspoilt nature of the Galley Reach mangroves and their wide range of environments and easy access from the capital Port Moresby favour their preservation for recreation and study.