Claim preclusion focuses on barring a suit from being brought again on an event which was the subject of a previous legal cause of action that has already been finally decided between the parties or those in privity with a party.
It is often difficult to determine which, if either, of these apply to later lawsuits that are seemingly related, because many causes of action can apply to the same factual situation and vice versa. The scope of an earlier judgment is probably the most difficult question that judges must resolve in applying res judicata. Sometimes merely part of the action will be affected, such as a single claim being struck from a complaint, or a single factual issue being removed from reconsideration in the new trial.
However, there are limited exceptions to res judicata that allow a party to attack the validity of the original judgment, even outside of appeals. These exceptions—usually called collateral attacks—are typically based on procedural or jurisdictional issues, based not on the wisdom of the earlier court's decision but its authority or competence to issue it. A collateral attack is more likely to be available (and to succeed) in judicial systems with multiple jurisdictions, such as under federal governments, or when a domestic court is asked to enforce or recognize the judgment of a foreign court.
In addition, in cases involving due process, cases that appear to be res judicata may be re-litigated. An example would be the establishment of a right to counsel. People who have had their liberty taken away (i.e., imprisoned) may be allowed to be re-tried with a counselor as a matter of fairness.
In order for a second suit to be dismissed on a motion of res judicata in a civilian jurisdiction, the trial must be identical to the first trial in the following manner: (1) identical parties, (2) identical theories of recovery, and (3) identical demands in both trials. In other words, the issue preclusion or collateral estoppel found in the common law doctrine of res judicata is not present in the civilian doctrine. In addition if all else is equal between the two cases, minus the relief sought, there will be no dismissal based on res judicata in a civil law jurisdiction.
While most civilian jurisdictions have slightly broadened the doctrine through multiple exceptions to these three requirements, there is no consensus on which exceptions ought to be allowed.
Note: Louisiana (USA), a civil law jurisdiction, has in the last twenty years, begun to follow the common law doctrine of res judicata.
Arguably, res judicata is a general principle of international law under Article 38 (1)(c) of the International Court of Justice Statute. "The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall apply: ... c. the general principles of law recognized by civilized nations".
Similar provisions are also found in the International Convenants on Civil and Political Rights, and Article 4 of Protocol 7 of the European Convention on Human Rights. However, in the two said conventions, the application of res judicata is restricted to criminal proceedings only. In the European Convention, reopening of a concluded criminal proceedings is possible if -
(a) it is in accordance with the law and penal procedure of the State concerned; (b) there is evidence of new or newly discovered facts, or (c) if there has been a fundamental defect in the previous proceedings,
which could affect the outcome of the case.
In India, concept of res judicata is contained in section 11 of the Code of Civil Procedure, 1908.