Due process of law is application by state of all legal rules and principles pertaining to the case so all legal rights that are owed to the person are respected. Due process balances the power of law of the land and protects the individual person from it. When a government harms a person without following the exact course of the law, this constitutes a due process violation, which offends the rule of law.

Due process has also been frequently interpreted as limiting laws and legal proceedings (see substantive due process) so that judges, instead of legislators, may define and guarantee fundamental fairness, justice, and liberty. That interpretation has proven controversial. Analogous to the concepts of natural justice and procedural justice used in various other jurisdictions, the interpretation of due process is sometimes expressed as a command that the government must not be unfair to the people or abuse them physically or mentally The term is not used in contemporary English law, but two similar concepts are natural justice, which generally applies only to decisions of administrative agencies and some types of private bodies like trade unions, and the British constitutional concept of the rule of law as articulated by A. V. Dicey and others. However, neither concept lines up perfectly with the American theory of due process, which, as explained below, presently contains many implied rights not found in either ancient or modern concepts of due process in England.

Due process developed from clause 39 of Magna Carta in England. Reference to due process first appeared in a statutory rendition of clause 39 in 1354 thus: "No man of what state or condition he be, shall be put out of his lands or tenements nor taken, nor disinherited, nor put to death, without he be brought to answer by due process of law." When English and American law gradually diverged, due process was not upheld in England but became incorporated in the US Constitution.