The article contains the results of the analysis of the development of res judicata doctrine into a multicomponent doctrine with different meaning in different legal systems of the world, as well as points out the difficulties of distinguishing this doctrine among other doctrines that have claim preclusive or issue preclusive effects. The article focuses on the broad and narrow meaning of res judicata, procedural links that this principle may have with the application of the estoppel rule in court proceedings. The article pays special attention to three doctrines related to res judicata: full faith and credit; election of remedies and law of the case doctrines. The doctrine of full faith and credit in the US procedural law is viewed as a branch of res judicata. In contrast to res judicata, the doctrine of election of remedies is largely based not on respect for the finality of the judgment, but on the principle of estoppel and thus might be applied in order to bar a subsequent cause of action containing claims that are inconsistent with remedies prayed for in the already considered cause of action, rather than to bar the relitigation of already litigated case. The law of the case doctrine, as it has been developed in the US procedural law and adopted in some other countries, in particular India, is related to res judicata in that both are aimed at ensuring legal certainty and the stability of court judgments. However, unlike res judicata, the law of the case doctrine to some degree allows the discretion of the court, or rather its application is discretion based, it is purely procedural and concerns the stability and consistency of the court's rulings in the same case, rather than the conclusive effect of the final judgment for subsequent proceedings. The article argues that these doctrines, especially the election of remedies doctrine and the law of the case doctrine or their elements can be used to address the problems of fairness and consistency of judgments in procedural law.