ABSTRACT
The aim of the first part of this chapter is to explore in general terms the theoretical foundations of today’s thinking. More detailed reviews can be found in other sources, for example Dulay et al. (1982), Selinker (1992), Thomas (2004) and Gass (2009). We will limit ourselves to the period since the 1950s, which has seen the development of theorizing about second language learning from an adjunct to language pedagogy, to an autonomous field of research. This period can itself be divided into three main phases.
