In the 12 years since Studies in Second Language Acquisition published its first thematic collection on L2 lexical issues, “The use and acquisition of the second language lexicon,” edited by S. Gass (1987), the centrality of lexical development in second language acquisition has received ever increasing recognition from researchers (see, for example, volumes by Arnaud & Béjoint, 1992; Coady & Huckin, 1997; Haastrup, 1991; Haastrup & Viberg, 1998; Harley, 1995, 1996; Hatch & Brown, 1995; Huckin, Haynes, & Coady, 1993; Meara, 1992; Nation, 1990; Schmitt & McCarthy, 1997; Schreuder & Weltens, 1993; Tréville, 1993; Tréville & Duquette, 1996). The 1987 collection was a leading foray into new territory, following a period of relative neglect of the lexicon in SLA. The issues taken up by its authors were quite diverse, ranging from the organization and components of the L2 lexicon, to aspects of acquisition such as cross-linguistic influence, restructuring, and rate, to L2 lexical-use issues such as retrieval and access. Since that time, a large body of L2 research and theory has developed around these and other topics, and it has become possible to deal comprehensively with single core issues in L2 lexical acquisition from multiple perspectives. The current collection is one such attempt, offering a set of related papers on the topic of incidental L2 vocabulary acquisition. Unlike the 1987 collection, which argued for recognition of the importance of the lexicon in a field dominantly concerned with the acquisition of syntax, the authors of the present collection assume the central importance of lexical acquisition.