Whilst the crime of murder, and its equivalents, is clearly defined and subject to extensive jurisprudence in every jurisdiction, no attempt has been made to give this crime a definition at the international level. For the international criminal tribunals, such as the ICTY, to work effectively, and fairly, this and other major crimes must be clearly defined from the outset. This paper briefly compares the approach to murder as a class of homicide across major legal systems. It reveals that, for all their differences, each system makes many of the same distinctions between classes of homicide, and provides us with similar conceptual tools to help us find a workable and just definition for this most serious of crimes.