ABSTRACT
Knowing how big our vocabularies are and how they develop is a key issue in both first and second language learning. In this chapter, we address three main questions: (1) whether learning vocabulary in the L1 is the same as doing it in the L2 or not; (2) how many words research says we know in first and second languages, making a difference between learning in naturalistic and in formal settings; and (3) how we measure vocabulary size and growth, focusing on different methodological aspects and several testing tools. The chapter also provides ideas on further research, which will need to deal with new assessment methods and growth simulations, as well as on languages other than English. The role of individual differences in L1 and L2 lexical development should also be brought back to the agenda.
