Social ties are the most important resource human beings have. Although other people can be difficult and challenging, they can also provide protection, solace, and social support, among other benefits. However, some relationships can be toxic and because these adverse conditions can be physiologically taxing, they can negatively affect both mental and physical health. Changes such as these can operate in large part through alterations in the sympathetic nervous system, the hypothalamic-pituitary-adrenal system, and the immune system. Much of the benefit of social support is perceptual and stems from the comfort of believing that supportive others can or will be there when times are stressful. The abilities to gain and perceive social support begin early in life and are heavily influenced by the climate of the family. Social support depends, in part, on reciprocity, yet many challenges to receiving support exist. Giving support to others has its own psychological and physiological benefits, although at intense levels, such as demanding caregiving responsibilities, these benefits dwindle. Moreover, social support needs change over time with changing circumstances. Public policy efforts to help people build and capitalize on their potential support networks is essential to maximize the impact of social ties on mental and physical health.