This chapter starts by exploring basic questions related to the learning of second language vocabulary such as What is a word? and What does it mean to know a word? It discusses form–meaning mapping as well as a word’s grammatical features and its collocations. The chapter focuses on different types of vocabulary knowledge including receptive knowledge, productive knowledge, breath and depth of knowledge, and knowledge related to multi-word units. The chapter refers to corpora as a way to understand how language functions in the real world. It also discusses different ways of learning new words, that is, incidental and intentional learning. The chapter moves onto issues related to the teaching of vocabulary, starting with explicit instruction involving memorization, and then moving on to more implicit activities (e.g., extensive reading). More specific techniques are reviewed such as glossing, corpus-based instruction, form-focused instruction, and strategy instruction.

Chapter 3 offers an interdisciplinary overview of research on multi-word units in second language (L2) processing and use. It is motivated by a long-standing puzzle in the field of second language acquisition suggesting that while the idiom principle is the main mechanism of language production in native speakers, non-native speakers cannot benefit from it to a similar degree. The chapter shows that researchers are not unanimous in assessing the degree to which learners operate on the idiom principle and raises a few problems which might be obscuring such operation in commonly used research designs, such as a focus on specific multi-word units rather than co-selection as such, questionable representativeness of reference corpora and inability of statistical measures to capture abstracted associations. The chapter concludes by offering an alternative interpretation based on the concept of approximation adopted from studies of English as a lingua franca.