This book provides a comprehensive overview of the theoretical issues and existing research in relation to the emotions that learners’ experience when learning and using a FL, highlighting the two emotions under investigation, enjoyment and anxiety, which are the focus of the empirical research reported later in the book. Highlighting the crucial role of emotions in the foreign language (FL) learning process, this book reports the findings of a study investigating the relationship between foreign language enjoyment (FLE) and foreign language anxiety (FLA) in the context of Polish secondary school students learning English as a FL. Chapter 1 conceptualizes emotions and introduces their different typologies. Chapter 2 looks at the constructs of FLE and FLA, while Chapter 3 presents findings from a selection of studies on FLE, FLA, and the relationship between them. Chapter 4 describes the rationale for conducting the study and includes a detailed description of the analytical procedures. It goes on to present the results of the study, the discussion, and the study limitations. Finally, Chapter 5 highlights the pedagogical implications of the study and suggests some directions for future research. The book is of interest to specialists researching the role of emotions in SLA, as well as to FL teachers looking for realistic recommendations for their work with FL learners.