As a Centre of Excellence, the Centre for Fertility and Health submits an Annual Report to the Research Council of Norway each year. This is their fourth annual report, for 2021. The Centre has continued to grow in 2021 and many new talented team members have been recruited. There has also been an increasing number of publications stemming from key projects that were initiated through the Centre of Excellence grant. The scientific goal of the Centre is to greatly advance the understanding of causes and health consequences of changes in patterns of fertility and family structure. The changing trends may influence child and adult health through social and biological pathways. To achieve this goal, the Centre combines expertise from epidemiologists, geneticists, physicians, demographers, statisticians, and economists. In this annual report, they provide a synopsis of their research in five integrated themes of research. They also present selected research findings and projects. Most of their research projects and activities are intertwined and form part of several research themes.