Abstract: Oecophylla species are among the most iconic tropical ants, but a broad review of their biology has been lacking. The two living species of Oecophylla are widespread in the Old World tropics and are similar in presenting the most sophisticated nest-building activities of all weaver ants. Workers draw leaves together, often forming long chains, and glue them together with larval silk. Chain formation promises to provide a major subject for the development of models of the self-organization of complex behavior. The colonies are very large and highly polydomous. Queens are predominantly though not exclusively once-mated and colonies are usually single-queened, but most Northern Territory (Australia) colonies are polygynous. The workers are highly polymorphic (seen also in a fossilized colony), show complex polyethism, and present a much-studied rich pheromonal repertoire for the colony's tasks. Colony odor is partly learned, showing a "nasty neighbor" effect in reactions to other colonies of this highly territorial ant, and partly intrinsic to each individual. The odor varies over time and differs between the nests of a colony. Not surprisingly, Oecophylla ants are hosts to a variety of inquilines, such as spiders, which mimic the colony odor to escape detection. In addition, a constellation of Homoptera benefit from ant protection, yet the activities of the ants in controlling pest species make these ants beneficial insects (they are also human food in some areas). We speculate that the existence of Oecophylla blocks other weaver ants from evolving highly complex social organization, an idea which could be tested with further knowledge on the timing of ant adaptive radiations.