Civil society plays a crucial role in the fight against corruption. The inclusion of civil society in the United Nations Convention against Corruption Implementation Review Mechanism (IRM), however, is only optional. This paper analyses the role civil society has played to date in the IRM in Bangladesh, Brazil, Croatia, and Zambia. The process was broadly perceived as an one-off technical exercise without clear connection to the fight against corruption. This is in large part due to the process being perceived as lacking transparency and civil society participation. The report identifies several opportunities to strengthen the role of civil society, including: 1) promote awareness of the IRM; 2) ensure sufficient time for meaningful public participation; and 3) develop specific policy advice and practical guidance aimed at ensuring broad public participation.