A Los Angeles, California city ordinance required any individual, living within the city limits, convicted of an offense “punishable as a felony” in the state or who would otherwise be punishable in the state if convicted in a different state, to register with the Chief of Police. No element of willfulness was included in the ordinance. Lambert (defendant) was charged with violating the ordinance. At trial, Lambert attempted to show that she had no knowledge of the requirement, but the trial judge refused to allow the evidence. Lambert was found guilty by a jury, fined $250, and sentenced to three years probation. Lambert appealed. The U.S. Supreme Court granted certiorari to determine whether the registration requirement violated due process where it applied to a person who did not have actual knowledge of the requirements and where no showing was made of the probability of such knowledge.