ABSTRACT. The segregation of Catholics and Protestants varies spatially and temporally in Belfast, Northern Ireland. Using small-area statistics from the censuses of 1971, 1981, and 1991, taken during the recent “Troubles,” a strongly rising level of ethnic segregation is noted for the 1970s, followed by a more gentle rise in the 1980s. Segregation is shown to vary among subunits of the urban area. The basic cause of this segregation is ethnic violence, and the spatial variation in segregation can be attributed to spatial variation in this violence.