Biological and chemical weapons are a realistic threat for the EU, which requires concerted effort to combat. The EU has sought to be active in this field by incorporating EU-wide export controls and having EU sanctions against individuals suspected of proliferation activities. However, in many regards the national measures of the member states of the EU are still quite divergent when it concerns chemical and biological weapons, especially regarding criminalization. This raises the question of whether continued convergence in this field is necessary. This submission will look at this by discussing the current activities of the EU in this field and contrasting this with the existing legislation in the 27 member states, with a focus on the criminal prohibitions. It will show the gaps that exist within the EU regulation as well as in the national legislation addressing biological and chemical weapons. Art. 83(1) TFEU allows for the harmonization of national criminal legislation in certain circumstances. While chemical and biological weapons cannot fully be captured under any of the existing areas of crime included in Art. 83(1) TFUE, these can be expanded. The existing gaps in the national penal provisions in combination with the EU-wide effects of any potential use or proliferation of chemical and biological agents warrants the expansion of the areas of crime and harmonisation of national criminal law on the basis of Art. 83 TFEU.