The following article aims to assess the applicability of “blank criminal laws” under positive legal systems, as well as the threat it represents for the nullum crimen sine lege principle. It discusses the approaches to this concept taken by different legal systems in Latin America, particularly in Guatemala, where this technique was recently used to include in a flagship sentence several Conventions in which the State is involved but which are not fully transcribed into the corresponding codes. “Blank criminal laws” are understood as incomplete laws that only establish a penalty, leaving it to another judicial rule the broader definition, and analysis. The article compares the application of such laws in different Latin American countries, and how each country addresses the possible collision with the principle of legality.