From the United Nations (UN) to the Group of Eight (G8), formal and informal international institutions entertain a wide array of options for encouraging member states to comply with institutional rules and norms. Scholars have largely overlooked one option in particular: membership suspension. For most international organizations (IOs), a rule for suspending an aberrant state was built into the founding mandate or charter as a means of enforcement. In practice, however, suspension has been infrequently used. As IOs have gained both autonomy from their members (Trondal and Veggeland 2014) and influence over them (Johnson 2014), there has been an increase in organizations’ use of membership suspension in response to states’ noncompliance. This increase is particularly evident in the 2000s. In 2011, for example, the League of Arab States (LAS) suspended Syria for the violence it committed against its citizens during its civil war. In 2014, the African Union (AU) suspended Egypt after the Egyptian military overthrew a democratically elected president, while the G8 suspended Russia for its intervention in Ukraine. This increase in frequency of suspensions is a puzzle because it coexists with another trend: a disparity in the use of suspension by different IOs to ensure accountability and compliance. Among IOs, the AU has most frequently suspended its members. One would have expected it to be the least likely organization to suspend given its post-colonial past and a historical reluctance to intervene in states’ domestic affairs. A second puzzle is why IOs have turned to this accountability mechanism; there is a lack of evidence indicating whether suspensions have a true accountability impact. In other words, their effectiveness remains uncertain. This chapter, therefore, seeks to address the question of why IOs suspend member states.