The thesis explores the interaction between affect and meta-cognition as conceptualised by Bachman and Palmer's (1996) model of language use. Anxiety is used to operationalize the concept of affect and develop an empirical model of interaction between meta-cognitive strategies, affect and language performance. The theoretical part examines the use of concepts of affect and meta-cognition in psychology and linguistics and the existing models of interaction between the two. Cognitive theories of affect and anxiety are reviewed to define the functions of affect in language use and provide the basis for the practical studies. The practical research is concerned with exploring the causes of foreign language anxiety and detecting the effects of foreign language classroom, test trait and test state anxiety on language performance. Meta-cognitive competence is explored using Purpura's (1999) Meta-cognitive strategy questionnaire. Research methods include an observation, two interviews and two questionnaire studies. The mathematical modelling method (SEM) is used to develop an empirical model of interaction between meta-cognition, anxiety and explore the impact of these variables on language proficiency.