Social isolation and loneliness in older adults are growing problems. Empirical research suggests that loneliness can lead to poorer health outcomes including higher mortality rates. Befriending has been shown to decrease loneliness and depression although the exact mechanisms of action are unclear. In this study we aimed to explore experiences and identify key ‘ingredients’ of befriending through interviews conducted with 25 older adults who had used five different befriending services across England. We used Berkman's theoretical model of how individual social networks impact on health to help interpret our data and explore the mechanisms of befriending for older adults. Findings suggest that befriending offers some compensation for loss of elective relationships from older adults’ social networks, providing opportunities for emotional support and reciprocal social exchange through development of safe, confiding relationships. Good conversational skills and empathy were the foundation of successful relationships within which commonalities were then sought. Befrienders broadened befriendees’ perspectives on life (particularly among older adults in residential care). Social engagement was a powerful mechanism of action, particularly in terms of connecting people back into the community, reinforcing meaningful social roles and connecting to a past life that had often been significantly disrupted by loss. Understanding key components and mechanisms of befriending for older adults may facilitate development of more effective and theoretically sound befriending services.