This special collection brings together research exploring and evaluating probabilistic variation patterns from a comparative perspective, thus highlighting current work situated at the crossroads of research on usage-based theoretical linguistics, variationist linguistics, and sociolinguistics. The contributions in the collection advance our understanding of the plasticity of syntactic knowledge on the part of language users with diverse regional and/or cultural backgrounds, and demonstrate how a probabilistic approach to grammatical variation can offer insight into the scope and limits of language variation. In this general introduction to the special collection, we provide some essential background for perspective, and subsequently summarize the contributions in the collection.