This chapter presents an overview of the current knowledge about burnout, a state of work-related mental exhaustion. It starts with the history and societal background of the phenomenon and discusses the concept and various definitions. Next, the assessment of burnout using questionnaires and clinical interviews is reviewed and an overview of its prevalence is presented. Potential antecedents (i.e., job demand and lack of job resources), consequences (i.e., physical and mental health, and organizational outcomes) and correlates (i.e., gender, personality factors) are discussed as well. Various descriptive models, such as the Job-Demands Resources model and the Six Areas of Working Life approach, are treated, as well as explanatory models that refer to lack of reciprocity and emotional contagion. Next, the effectiveness of individual and organizational interventions to prevent and reduce burnout is evaluated. The chapter closes with an outlook that includes future research challenges and emphasizes the importance of distinguishing mild burnout symptoms that refer to unwell-being from severe symptoms that are indicative for a burnout disorder.