More than a decade has passed since the establishment of the two ad hoc Tribunals, however, the jurisprudence of both Tribunals evidence the inconsistency regarding the requisite mens rea standards for serious violations of international humanitarian law. Hence, a survey of the attitude taken towards the definition of the major facets of mens rea by the world major legal systems is of great significance with regard to the establishment of a unified concept for mens rea in international criminal law. Section I of this study examines some of the major judgments of the two ad hoc Tribunals where both Tribunals refers to national jurisdictions in order to clarify the mens rea required for the imposition of criminal responsibility for serious violations of international humanitarian law. Section II is a brief outline of the structure of the criminal offence in German criminal law. This is necessary since German criminal law does not follow the “offence analysis” scheme known in common law countries, but is based upon a three stage structure of the criminal offence. In Section III, the concept of intention (Vorsatz) in German criminal law is thoroughly discussed and analysed. This includes the discussion of dolus directus (first and second degree) as well as of dolus eventualis. Emphasis is put on the differentiation between dolus eventualis and negligence, since it reflects a highly debated issue in German criminal law. The concept of negligence will be outlined in Section IV. Given the fact that the German criminal law recognizes that mistake of law and mistake of fact (Tatbestandsirrtum, Verbotsirrtum) is not a separate doctrine, but part and parcel of the basic analysis of mens rea, these two basic types of mistake will be addressed in Section V. This includes the discussion of error in persona vel obiecto and aberratio ictus. Finally, the conclusion will be supported by some remarks and recommendations regarding the German law of intent and its influence on the development of international criminal law.