46 | Chapter 12 INTRODUCTION AND RESEARCH QUESTION The social significance of sport has increased substantially in the past decades. This is in part because of the rapid expansion of sport offerings and greater differentiation in sport activity (Borgers et al., 2018; Klostermann & Nagel, 2014). An additional factor is the increasingly functional view of sport “as a means”, for example, to promote public health (Miles, 2007) and “healthy aging” (Bauman et al., 2016), to contribute to children’s socialisation and to enhance social cohesion (Putnam, 1995; Seippel, 2006). It is therefore understandable that creating possibilities for safe and nearby sport participation for everyone (“sport for all”) has become a priority in policies of and for entities related to sport, such as - in the Netherlands - the Ministry of Health, Welfare and Sport (Ministerie van VWS, 2017), the “Dutch Olympic Committee & Dutch Sports Federation” (NOC*NSF, 2017) and the “Association of Sports andMunicipalities” (VSG, 2018). Because there are many kinds of sport to choose from, organised in a variety of different ways, individuals can select the sport activity that suits them best. Inevitably people’s desire to take part in sport and their opportunities for doing so change over the life course. A sharp decrease in regular (i.e., at least 12 times a year) and frequent (i.e., at least 40 times a year) participation in sport activities over the life course was found, from, respectively, almost 90% (regular) and 75% (frequent) among teenagers to less than 20% (regular) and 15% (frequent) among octogenarians. Moreover, those who did continue to participate in sport were less likely to do so in a club setting as they grew older (Tiessen-Raaphorst, Verbeek, De Haan, & Breedveld, 2010). This drop in sport activity has been linked, among other things, to age-related “physical decline”, such as bodily problems and illnesses (Van den Dool et al., 2009). Moreover, people experience many major life events during their lifetime: they might marry, get a job, have children and retire. It is therefore relevant to ask whether these life events have particular consequences for participation in sport. This chapter addresses that question. An individual’s life course can be seen as a series of stages that a person passes through, with each life stage presenting new patterns of opportunities and constraints for sport participation. This suggests that participation in sport may differ per life stage (Engel & Nagel, 2011; Pilgaard, 2013; Tiessen-Raaphorst et al., 2010). The transitions between these stages are “socially critical periods”