In contemporary European societies, individuals’ lifecourses and family structures are constantly changing and becoming less standardized. Cross-nationally comparative and longitudinal data provide unique opportunities to study how societal processes influence demographic choice. The Generations and Gender Programme (GGP) is a social science research infrastructure that provides panel data on the whole lifecourse of 280,000 individuals from more than 20 European and non-European countries. It includes data on intergenerational exchange and support and the timing and sequence of key demographic transitions. In this chapter, the authors outline the GGP’s contributions to understanding today’s relationships and lifecourse processes. They also illustrate the innovations and advantages of the new round of data collection, starting in 2020.