Lexical knowledge is complex, multidimensional, and difficult to pin down to a set of defined components. The development, organization, and use of lexical knowledge in the first and additional languages are studied in a number of neighbouring disciplines beyond second language acquisition and applied linguistics, including psycholinguistics, neurolinguistics, computational linguistics, and language education. In this introduction, we highlight how the five articles in this special issue hone our understanding of different aspects of second language (L2) lexical knowledge, its acquisition, and use by adopting innovative research design, methods, and approaches to data collection and analysis from these distinct but related disciplines, affording new theoretical and empirical insights.