Crime is an act or omission that the law makes punishable. It can also be the breach of a legal duty, which is treated as the subject matter of a criminal proceeding. There are serious and less serious crimes. However common law recognizes only two classes of crimes- serious crimes or felonies and minor crimes or misdemeanors. There are different types of crimes like administrative crime, white collar crime, hate crimes and the like. Mens Rea (guilty mind) and Actus Reus (guilty act) are two important elements that are necessary to prove a crime.