Lexical skills are a crucial component of language comprehension and production. This paper reviews evidence for lexical-level deficits in children and young people with developmental language impairment (LI). Across a range of tasks, LI is associated with reduced vocabulary knowledge in terms of both breadth and depth and difficulty with learning and retaining new words; evidence is emerging from on-line tasks to suggest that low levels of language skill are associated with differences in lexical competition in spoken word recognition. The role of lexical deficits in understanding the nature of LI is also discussed.