Over the past years our group has been working on a coherent research program on the relationships between greenspace and health. The main aims of this “Vitamin G” program (where G stands for green) were to empirically verify relationships between greenspace in residential areas and health and to gain insight into mechanisms explaining these relationships. In this article, we bring together key results of our program regarding the relevance of three possible mechanisms: stress reduction, physical activity, and social cohesion. The program consisted of three projects in which relationships between greenspace and health were studied at national, urban, and local scales. We used a mixed-method approach, including secondary analysis, survey data, observations, and an experiment. The results confirmed that quantity as well as quality of greenspace in residential areas were positively related to health. These relationships could be (partly) explained by the fact that residents of greener areas experienced less stress and more social cohesion. In general, residents of greener areas did not engage in more physical activity. The article concludes with a discussion of the practical implications of these findings and identification of areas that need more in-depth research.