The core aim of this Article is to analyse whether it was an appropriate decision from a criminal policy perspective to adopt the Environmental Crime Directive. The Article asks the basic question whether the Union should enforce Union environmental law by means of criminal sanctions. In this regard it is claimed that, according to the principle of ultima ratio, the Union legislator may only require that an act is criminalised if it is necessary to protect a fundamental European interest, and only on the condition that all other measures have proved insufficient to safeguard that interest. The Article therefore examines whether criminal law measures is suitable for the enforcement of Union environmental rules and secondly if there are other measures which are equally effective in enforcing Union environmental law as criminal sanctions.