ABSTRACT
Individual learners can differ with regard to the breadth (the number of known words) and depth (how well words are known) of their second language (L2) vocabulary knowledge. This chapter focuses on common individual difference (ID) factors that can explain variability in L2 vocabulary learning. It synthesizes ID research findings, discusses how vocabulary learning is influenced by these IDs, and describes the instruments to elicit ID data in L2 vocabulary research. Although ID research on L2 vocabulary learning has gained renewed interest, there is considerable room for further research on some of the ID factors in L2 vocabulary research.
