The study of personality has long been one of the major themes in Psychology. Nevertheless, within the field of Second Language Acquisition (SLA), this research area has not received a lot of recognition, despite the strong ties of both disciplines. The objective of this paper is to describe the concept of personality and its role within the SLA field, as well as to outline the dominating research methodologies that are based on distinctive theoretical approaches. For this purpose, in Section 1 of the paper, the basic term of personality is defined, and its role in the process of foreign language acquisition is described, together with an outline of the most frequent problems encountered in the empirical studies of the concept therein. Sections 2 and 3 are devoted to the outline of the dominant theories of the study of personality: type and trait approaches. They are completed with a presentation of the most popular inventories and measuring scales assessing the concept in question that could be reliably applied in SLA research.