Most transnational criminal law treaties do not benefit from any sort of monitoring mechanism that would allow states parties or other actors to assess their domestic implementation and enforcement. There are a few exceptions, as treaties and other instruments concerning drug control, corruption, and money laundering are indeed accompanied by monitoring mechanisms. But the general pattern across the field of transnational criminal law is clear. This article explores some possible explanations for why transnational criminal law treaties generally lack monitoring mechanisms, and it also highlights the significance of this absence from a compliance perspective. The article advocates not for the creation of more treaty monitoring bodies in the field of transnational criminal law, but instead seeks to explain their relative absence and its significance for the field. The argument, therefore, is not that monitoring bodies are necessarily desirable and ought to exist in greater numbers in this field, but rather that the absence of these bodies obscures information about compliance and impedes research about what these treaties are actually accomplishing. The current state of treaty monitoring in the field of transnational criminal law is significant because of the extent of what we do not know about the effects of these instruments.