In criminal law, the principle of legality is the maximum premise that governs any process, limits the interpretation of criminal definitions, requires their pre-existence in order to prosecute an offender, prevents their retroactive application and demands proportionality in the punishment imposed.At the level of international criminal law, the normative development has been so limited and the criminal offenses have been so poorly defined, conceptualized and specified that, in strict adherence to the principle of legality, many defendants would have been acquitted. Moreover, even the largest international trials in the history of mankind were supported, at least in some way, in the slight or crass obviousness of certain postulates of the principle of legality, because in view of the poor international criminal normative development, it becomes practically imperative the need to expand or extend the interpretation of the existing criminal types, which in Criminal Law is prohibited