Lambert v. California, 355 U.S. 225 (1957), was a United States Supreme Court case regarding the defense of ignorance of the law when there is no legal notice.

The ordinance stipulated that she, as a convicted criminal, could be fined $500 and sentenced to up to six months in jail for every day that she remained in the city after the five-day limit.

Lambert appealed her case, arguing that she had no knowledge that she had to register her name and that convicting her would deprive her of due process under the Fourteenth Amendment.

Justice William Douglas, who delivered the majority opinion for the Court, wrote: Where a person did not know of the duty to register and where there was no proof of the probability of such knowledge, he may not be convicted consistently with due process.

Nevertheless, this appellant, on first becoming aware of her duty to register, was given no opportunity to comply with the law and avoid its penalty, even though her default was entirely innocent.