Previous research from the United States suggests that volunteers’ time contributions have declined during a period when participation rates have risen. Scholars have offered various possible explanations for this trend, including generational differences, socio-economic changes, and family life changes. In Europe, previous research has shown that participation rates have risen in most countries, but little work has addressed trends in volunteers’ time contributions. In this article, we use survey data from Denmark merged with data from administrative registers covering the 2004–2012 period to show that, similar to the trend in the United States, Danish volunteers’ time contributions have declined as participation rates have risen. Our results suggest that this decline is partially explained not by socio-economic or family life changes but by weakening organizational attachment measured by a decline in volunteers’ propensities to be members of the organizations for which they volunteer. On these grounds, we argue that an important consequence of weakening organizational attachment is that volunteers’ contributions of time decline.