Marrying Durkheim’s definition of the social fact (1895) with Gumperz’ classic framework for studying the speech community (1968), the paper argues that these concepts are crucial to the 21st century sociolinguistic enterprise. It explores the basic dimensions of variation across speech communities, illustrating their applicability to communities of several different types. These include monolingual communities where speakers have a common base in linguistic structure as well as complex multilingual communities with internal social divisions. Illustrations are drawn from the author’s research in French Canada and Papua New Guinea, and from Blanc’s (1964) study of Baghdad. Finally, the study of multilingual speech communities is linked to the understanding of how superposed linguistic knowledge is integrated across the lifespans of individual speakers and across communal groups. Even in such situations, members who do not share a language seek to communicate with each other, finding ways of doing so that respond to social opportunities and circumvent social barriers.