Criminalization or criminalisation, in criminology, is "the process by which behaviors and individuals are transformed into crime and criminals". Previously legal acts may be transformed into crimes by legislation or judicial decision. However, there is usually a formal presumption in the rules of statutory interpretation against the retrospective application of laws and only the use of express words by the legislature may rebut this presumption. The power of judges to make new law and retrospectively criminalise behaviour is also discouraged. In a less overt way, where laws have not been strictly enforced, the acts prohibited by those laws may also undergo de facto criminalisation through more effective or committed legal enforcement.