This subject aims to provide students with a detailed, specific and up-to-date vision of the different theories relating to the learning and teaching of a foreign language. Some of the most relevant theories about the acquisition of second languages will be reviewed in order to provide a theoretical foundation which will allow them to reflect on the learning process and at the same time prepare them to incorporate some of the most important concepts in their own teaching practice. In addition, the subject includes a description and analysis of the most relevant affective factors which are involved in the learning process: age, motivation, intelligence (Multiple Intelligence Theory), aptitude, etc.