California’s Unpredictable Res Judicata (Claim Preclusion) Doctrine

The doctrine of res judicata describes a set of rules that determine the preclusive effects of a final judgment on the merits. The California doctrine has two familiar components: a primary aspect, “res judicata” or claim preclusion; and a secondary aspect, “collateral estoppel” or issue preclusion. Under the claim preclusion aspect, a prior judgment bars the parties (or those in privity with them) from relitigating the “same cause of action” in a subsequent proceeding. Under the issue preclusion aspect, although a second suit between the same parties on a different cause of action is not precluded by a prior judgment, the first judgment operates as a conclusive adjudication as to such issues in the second action as were “actually litigated and determined” in the prior proceeding.