Available open access digitally under CC-BY-NC-ND licence. This book offers a comprehensive analysis of why and when member states threaten to withdraw from regional international organizations (RIOs). A unique dataset covers over 120 exit threats across RIOs from all world regions. The book explains variation as a result of limited specific and diffuse support, such as the inability to exert influence or prevail under majority decision-making, as well as a lack of democratic socialization. With nationalism and populism on the rise, this timely study unpacks crucial pressure points in international institutions, offering invaluable insights into how they can maintain stability in the face of internal contestations.