This Manual introduces the role and impact of successful evidence gathering and processing in combating illegal, unreported and unregulated (IUU) fishing and describes the pillars for evidence gathering – the national legislation and regional and international obligations. Procedures for gathering the evidence are presented and requirements for arrest are described. The process for prosecutions and administrative procedures are elaborated and follow-up actions described, including IUU vessel listing. Challenges in evidence gathering and advice on how to overcome them are described.