Lists of landmark court decisions

Landmark court decisions, in present-day common law legal systems, establish precedents that determine a significant new legal principle or concept, or otherwise substantially affect the interpretation of existing law. "Leading case" is commonly used in the United Kingdom and other Commonwealth jurisdictions instead of "landmark case", as used in the United States.^[1][2]

In Commonwealth countries, a reported decision is said to be a leading decision when it has come to be generally regarded as settling the law of the question involved. In 1914, Canadian jurist Augustus Henry Frazer Lefroy said "a 'leading case' [is] one that settles the law upon some important point".^[3]

A leading decision may settle the law in more than one way. It may do so by:

• Distinguishing a new principle that refines a prior principle, thus departing from prior practice without violating the rule of stare decisis;
• Establishing a "test" (that is, a measurable standard that can be applied by courts in future decisions), such as the Oakes test (in Canadian law) or the Bolam test (in English law).
• Sometimes, with regard to a particular provision of a written constitution, only one court decision has been made. By necessity, until further rulings are made, this ruling is the leading case. For example, in Canada, "[t]he leading case on voting rights and electoral boundary readjustment is Carter. In fact, Carter is the only case of disputed electoral boundaries to have reached the Supreme Court."^[4] The degree to which this kind of leading case can be said to have "settled" the law is less than in situations where many rulings have reaffirmed the same principle.