Well-being is a widely used concept to characterize differences in how well students are feeling and doing. Yet, numerous conceptualizations of well-being exist, which hampers conceptual and empirical research on student well-being, and the development of measurement instruments of and interventions on students' well-being. To advance research and practice, we propose a definition and conceptual framework of student well-being that may serve as a basis for measuring, understanding, and promoting students’ well-being. We formulated four guiding postulates based on philosophical underpinnings of established perspectives on well-being that guided the development of our definition and framework, which was further shaped by existing literature and the input from meetings with experts. We define student well-being as a multi-facetted concept that reflects a student's degree of positive or negative cognitive appraisal about and affective experience with the self. Student well-being comprises seven interrelated facets (i.e., meaning in life, self-esteem, autonomy, relatedness, sense of belonging, subjective health, body acceptance) grouped into three domains: psychological, social, and physical. The conceptual framework outlines predictors and outcomes of student well-being. We discuss implications of our definition and framework for science and practice, as well as outline several key avenues for future research on student well-being.