Abstract The aim of this introductory article is to provide a background to the articles contained in this special issue of Lingua that centers around variation in form, variation in meaning, and markedness. Theoretical and empirical considerations are brought together in this special issue in which the linguistic disciplines that are covered diverge. The different contributions deal with language processing, first language acquisition, language contact, functional-typology and generative morphology and syntax. Several papers in this special issue argue in favour of an Optimality Theoretic analysis of the data under discussion. This is not a coincidence, given that Optimality Theory is claimed to be a formal theory of markedness (cf. Gilbers and De Hoop, 1998 , Lingua, 104, 1 for an introduction to OT). In Section 1 , we present two hypotheses dealing with the relation between variation in form and variation in meaning. We discuss several dimensions along which markedness of forms and meanings can be measured in Section 2 . In the final section we discuss the possibility that the concept of bidirectional optimization accounts for markedness as well as variation in form versus variation in meaning.