A criminal law may be changed owing to various reasons. Obsoleteness, loopholes and insufficiency of penalties on the part of the existing criminal law are some of the justifications which may warrant its amendment or replacement. Even though changing a criminal law following changes in circumstances is vital and advisable, the advent of a new criminal law may create the difficulty of determining the temporal scope of application of the former and the new laws. An interesting solution for such problem is the principle of nonretroactivity of criminal law, which states that a criminal law is applicable only to offences committed subsequent to its enactment. Nevertheless, this principle has some exceptions, which allow the retrospective application of a criminal law.