Unlike many recent books on L2 vocabulary and processing, this volume does not set out to offer a complex perspective of the L2 lexicon, but rather represents a sustained attempt to come to grips with some very basic questions clustered around the relationship between the L2 mental lexicon and the L1 mental lexicon. It provides a substantial review of L1 and L2 lexical research issues such as similarities and differences between the conditions of L1 and L2 acquisition, the respective roles of form and meaning in L1 and L2 processing, and the degree of separation/integration between L1 and the L2 lexical operations. New research into the L2 lexicon from the Trinity College Dublin Modern Languages Project is considered in the latter part of the volume.