For a long time, linguists more or less denied the existence of individual differences in grammatical knowledge. While recent years have seen an explosion of research on individual differences, most usage-based research has failed to address this issue and has remained reluctant to study the synergy between individual and community grammars. This paper focuses on individual differences in linguistic knowledge and processing, and examines how these differences can be integrated into a more comprehensive constructionist theory of grammar. The examination is (...) guided by the various challenges and opportunities that may be extracted from scattered research that exists across disciplines touching on these matters, while also presenting some new data that illustrate how differentiation between individuals can improve models of long-term language change. The paper also serves as the introduction to this special issue of Cognitive Linguistics, which collects seven contributions from various linguistic disciplines focusing on key aspects of individuals’ grammars. (shrink)