Key Points• Increasing evidence shows the behavioral, perceptual, and biological pathways by which social relationships and social networks positively impact health outcomes, including those for the aging mind and brain The facilitation of healthy aging, in turn, has been shown to increase social participation among older adults through community-based interventions and contributes to societal well-being.• "Healthy Aging" as Physical, Mental, and Social Well-Being The World Health Organization (WHO) defines health as "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity."l This definition emphasizes the importance of quality of life and social well-being and highlights the need to consider the impact of the social environment on human health. Public health interventions that target both the individual and his or her social environment embrace a holistic, ecological perspective that is very important for healthy aging. The ecological model posits that changes in the social environment will produce changes in the individual by addressing not only individual factors, but also inrerpcrsonal, organizational, community, and policy factors that support individual behaviors? With respect to aging, active engagement in social settings, or the social environment, is an important factor leading to productive and "successful aging.,,3 Although the process of aging is inevitable, epidemiological studies clearly show that the diseases and disabilities often associated with aging are not. Many of these "aspects of usual aging can be avoided or re\·ersed w l-,5 which suggests "chronological age per se is a relatively weak explanatory variable in assessing the prospects of continuing to age well in later life.,,6 Social relationships affect human immune function,7-9 brain activity, 10 and stress rcsponse.t ' Therefore, attempts have been made to enhance social integration among older adults, 12 exemplified by the inclusion of "active ageing" as a WHO goal for policy and program formulation. 13 The vVHO defines "active ageing" as "participation in social, economic, cultural, spiritual and civic affairs, not just the ability to be physically active or participate in the labour force. ,,13 By enabling older adults to remain productive and fully engaged, our society will continue to benefit from the resources this rapidly growing segment of the population provides.The impact of the social environment and relationships on individual well-being is greater in older age versus younger. 14 ,15 Support provided by family and friends becomes increasingly important especially when age-related diseases and disability OCClli. Nevertheless, age-related physical and functional decline can limit individuals' ability to maintain social relationships. Thus, it is important that we understand social network and relationship factors that influence, and are influenced by, the well-being of older adults. Such an understanding can enhance the development of interventions to prevent or delay the on...