The Unit for Advanced Studies in Modern Swedish (FUMS) at Uppsala University has one of the largest collections of spontaneous present-day spoken Swedish and has housed many sociolinguistic research projects since the 1960s. The four studies generating the most empirical data are on: The Urban Dialect of Eskilstuna; The Child's Linguistic Identification; Language, Roles, and Social Relations; and Town and Hinterland: Urbanization and Language. Despite their different areas of study, all four projects have attempted to describe sociolinguistic variation and identify its causes at the phonological and morphological levels. All have found considerable inter- and intra-individual variation at the structural levels examined and support the idea that this variation is greater in informal than formal situations. In turn, they have reinforced the importance of studying impromptu speech. (MSE)