The telecommunications industry is particularly competitive and characterized by very high churn rates. The literature on the topic is vast, but studies on the determinants of churn behavior are dispersed, failing to provide a comprehensive view of the state of the art. Based on this research gap, this article aims to contribute to developing the literature on customer churn in the telecommunications sector by summarizing the current state of research, and identifying the main determinants of churn and switching intentions. It provides a systematic literature review (SLR) of 37 articles on the topic published between 1999 and 2022. The results reveal the existence of two research streams. The first, in which the studies are based on surveys examining the alleged intentions of subscribers to change operators, with criteria such as satisfaction and attitudes as predictors, and the second, dealing with subscribers’ actual switching behavior and relating this to behaviors and characteristics extracted from internal customer management systems. All independent variables used to explain switching intention or real churn were mapped. It was found that age, gender, satisfaction, switching costs and barriers, and service quality are the most important determinants highlighted by the literature. Our study also outlines some insightful practical implications, which could be extended to other service sectors. The paper ends with a research agenda for future studies according to the gaps detected by the study’s results. Among its limitations, this research excludes papers related to predictive models and studies not in English.