Smuggling of migrants exposes migrants to the risk of severe human rights violations, causes the loss of thousands of lives and undermines the integrity of national borders. Because smuggling of migrants is an illegal activity, with a transnational and often clandestine character, data on its magnitude is limited. The number of detections of irregular border-crossings and unauthorized stays are not truly indicative of the scale of the phenomenon. The nature of smuggling of migrants, and the difficulties in accurately assessing its characteristics and scale, means that a criminal justice response must be both multifaceted and flexible, with an emphasis on inter-agency and international cooperation. Relevant approaches include (i) promoting robust investigations and prosecutions, (ii) enhancing information gathering, sharing and analysis, (iii) protecting vulnerable migrants more effectively, and (iv) enhancing international cooperation. The complex dynamics of smuggling of migrants calls for a holistic response that combines criminal and non-criminal justice responses. This Module focuses on the former, while Module 4 explores the latter.