1 | 9 Synthesis besides interpersonal disparities (i.e., differences between individuals) in sport participation, intrapersonal differences (i.e., individual changes) in sport participation during the life course are an important research topic (Engel & Nagel, 2011; Pilgaard, 2013; Pulles & Wendel-Vos, 2018; Tiessen-Raaphorst et al., 2010). This raises the question: why do individuals change their sport participation during their life course? To get an answer to this question, it is important to consider that people experience various major life events during their life, which are expected to affect sport participation and thereby might explain differences and changes in sport participation over the life course. For example, on a typical day in the Netherlands 4891 people move houses, 322 young adults start living on their own and 250 start to cohabit with their partner, 176 couples get married, 54 couples enter into a civil partnership, and 462 women give birth to a child (Statistics Netherlands, 2021c). In addition, according to the most recent data on labour market characteristics, 104,830 people obtained a bachelor’s or master’s degree in the academic year 2016/2017, of which 82,560 entered the labour market after graduation, and 76,420 of them started working within a year after graduating (Statistics Netherlands, 2021a). Furthermore, over 94 thousand employees retired in 2020 (Statistics Netherlands, 2021b). However, little is known about whether such major life events have particular consequences for participation in sport over the life course. I address this question in this dissertation by examining to what extent major life events affect the sport participation of individuals in the Netherlands. To this end, I conduct four empirical studies that examine the influence of major life events on individual sport participation from a life-course perspective. I pay specific attention to the transition to adulthood, as sustaining sport participation during this transition seems particularly challenging (Hirvensalo & Lintunen, 2011; Malina, 2001; Telama, 2009; Vanreusel et al., 1997). This period in life is often associated with a low stability of and sharp decline in individual sport participation (Engel & Nagel, 2011; Hirvensalo & Lintunen, 2011; Leslie et al., 2001; Van Tuyckom, 2011), and a high likelihood of dropping out, especially of club-organised sport (Borgers et al., 2016b; Eime et al., 2016; European Commission, 2018; Lunn, 2010; Pilgaard, 2013; Scheerder et al., 2006; Vandermeerschen et al., 2016). Moreover, the transition to adulthood is for many people a “socially critical period” of key individual life events, which might induce differences between and changes within individual sport careers and introduce breaches in the continuity of sport participation: they move out