Social connections are foundational to societal health and well-being, and their absence incurs significant social and economic costs. Social connections – the time people spend with each other, the support they give and receive, and the quality and diversity of their relationships to one another – improve our physical and mental health, enhance job satisfaction and cooperation, and strengthen community bonds. The reverse is also true, in that social isolation, loneliness and disconnection can have serious health consequences, straining already overburdened healthcare systems, harming labour market participation and discouraging civic participation. A growing number of OECD governments are recognizing this, and have introduced strategies that explicitly aim to foster connection. The OECD is launching Social Connections and Loneliness in OECD Countries, the first international report to provide a comprehensive comparative assessment of the state of social connections across OECD countries. It draws from high-quality official data sources to compare the quantity and quality of social connections across population groups and tracks how these outcomes have developed over in recent years. Importantly, it also identifies who is most vulnerable to isolation and loneliness – including the elderly, those who live alone, and those experiencing financial precarity – as well as newly emerging at-risk groups, such as men and young people. Given that social connections are in part shaped by structural conditions and policy choices, the report also highlights the importance of community-level interventions, including, for example, improving access to social infrastructure.