This paper provides the first overview of sea turtles in Guinea-Bissau, presents data on their ecology, and analyzes threats and conservation initiatives. The green turtle (Chelonia mydas) is by far the most widespread and abundant of the 5 species that nest in Guinea-Bissau. Between ca. 7000 and 29,000 green turtle nests are laid per year at the globally important site of Poilão Island, with a few hundred more on surrounding islands. There is a marked interspecific variability in nesting seasonality, with green and hawksbill (Eretmochelys imbricata) turtles nesting mostly during the rainy season and olive ridley (Lepidochelys olivacea) and leatherback turtles (Dermochelys coriacea) during the dry season. Informal interviews all over the coastal zone suggest that sea turtle populations have markedly declined within living memory. Main threats are poaching of eggs and of nesting females and the incidental capture in fishing gear. Amongst the major achievements of sea turtle conservation efforts are that all species are protected by law, the most important nesting beaches have been included in the protected area network, and significant progress has been made in removing the presence of settlements of foreign fishermen from the areas near the turtle concentrations where accidental captures used to occur. On the down side, it should be pointed out that protection in the national parks is insufficient. The main problem seems to be the weak enforcement of park and national rules by park authorities, which creates a feeling of relative impunity in park residents and visiting fishermen.