In this paper we attempt to define the notion of ‘lexeme’ in relation to signed languages. We begin by defining signs as a distinct kind of visual-gestural communicative act, different from other communicative uses of gesture. This is followed by a discussion of the most important categories of productive forms in signed languages, referred to simply as signs. The close relationship between the formational aspects of these signs and their meaning is also discussed and exemplified. We then describe the criteria for recognizing lexemes as a subset of signs, and distinguishing variant and modified forms. The paper concludes with a discussion of the implications the notion of lexeme has for our understanding of the lexicon of signed languages and for signed language lexicography.