This study uses data from recent household surveys in 43 developing coun- tries to describe the main dimensions of household size and composition in the de- veloping world. Average household size varies only modestly among regions, rang- ing from 5.6 in the Near East/North Africa to 4.8 in Latin America. These averages are similar to levels observed in the second half of the nineteenth century in Europe and North America. About four out of five members of the household are part of the nuclear family of the head of the household. Household size is found to be positively associated with the level of fertility and the mean age at marriage, and inversely associated with the level of marital disruption. An analysis of trends and differen- tials in household size suggests that convergence to smaller and predominantly nuclear households is proceeding slowly in contemporary developing countries.