In order to develop an effective criminal justice response, it is crucial to truly understand the phenomena at hand. The analysis of the two phenomena singled out for this contribution -namely trafficking in persons and smuggling of migrants -will be focussed at trying to understand the nature and extent of the involvement of organised criminal groups therein.To that end, this article explores what we know, what we do not know and what we should know about the involvement of organised criminal groups in trafficking in persons and smuggling of migrants. The relationship between organised crime and trafficking in persons , and the relationship between organised crime and smuggling of migrants, is taken into consideration on a multitude of levels. Additionally, serving as a significant counter-weight for organised involvement, it is stressed that a significant role is reserved for un-organised criminality in these phenomena. Because of its importance, this aspect is equally explored and its consequences for criminal justice responses are analysed. On the basis of the findings of enormous variety in criminal involvement in both trafficking in persons and smuggling of migrants, criminal justice responses are in high need of re-consideration.