In the past decades, the process of European integration has influenced all fields of law, including criminal law. Whereas the creation and enforcement of criminal liability used to be purely a national matter, European legislation now requires Member States to criminalize all sorts of harmful conduct. However, this legislation does not determine the full scope of criminal liability, omitting to define general principles of criminal law. For example, the European Union refers to 'intention' in its legislation, but it has not determined what qualifies as such. As a result, what is criminal in one Member State may not be criminal in another, which runs counter to the goal of harmonization. In order to remedy this, this book establishes what mens rea and defenses should look like in European criminal law. Should intentional conduct also encompass those consequences that were not wanted, but merely foreseen as possible side-effects? Should the European legislator be allowed to criminalize conduct that does not require any proof of mens rea? What justifications and excuses could a defendant raise in court? Can torture or murder ever be excused? To answer these questions, the book infers common principles of mens rea and defenses from European law and the legal systems of the Member States. Subsequently, it merges them into one coherent and enforceable system.