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 by civil society respondents as lacking transparency and meaningful venues for participation. The report identifies several opportunities to strengthen the role of civil society, including: 1) promoting awareness of the IRM; 2) ensuring sufficient time for meaningful public participation; and 3) developing specific policy advice and practical guidance aimed at ensuring broad public participation.