The aim of this investigation was to develop an instrument assessing the functions of self-talk (ST) in sports. Two studies were conducted for the development of the Functions of Self-Talk Questionnaire (FSTQ). In the first study, a prospective instrument was developed based on empirical evidence and a series of preliminary exploratory factor analysis. The results supported a five-dimensional 25-item solution. In the second study, the psychometric properties of the new questionnaire were tested. Confirmatory factor analysis (CFA) confirmed the hypothesized factor structure of the FSTQ. Furthermore, reliability analyses provided further evidence regarding the psychometric integrity of the instrument. The results of the study provide preliminary evidence regarding the multidimensionality of ST functions, suggesting that ST in sports can serve to enhance attentional focus, increase confidence, regulate effort, control cognitive and emotional reactions, and trigger automatic execution. The FSTQ seems a psychometrically sound instrument that could help with enhancing our understanding regarding the use and effectiveness of ST. (Contains 4 tables.)