Res judicata is the generic term for a group of related concepts concerning the conclusive effects given final judgments. Within this general doctrine there are two principal categories: (1) claim preclusion—also known as res judicata; and (2) issue preclusion—also known as collateral estoppel.

These legal doctrines generally preclude litigants from relitigating claims and issues that were previously litigated to a final resolution or judgment.

In Colorado, res judicata, also known as claim preclusion, prevents a party from relitigating a claim that has already been finally decided by a competent court. Once a final judgment has been rendered, the same parties cannot bring a lawsuit on the same claim or cause of action again. This principle promotes judicial efficiency and finality in legal proceedings. Issue preclusion, or collateral estoppel, is a related concept that bars the relitigation of specific issues that were already decided in a previous lawsuit between the same parties, even if the current lawsuit is based on a different claim. Both doctrines are grounded in the idea that once a matter has been adjudicated, it should not be reopened except under exceptional circumstances, such as the discovery of new evidence that could not have been obtained with reasonable diligence before. These principles are codified in Colorado's statutes and case law, and they are fundamental to the state's judicial system to ensure fairness and consistency in legal proceedings.