“Res judicata” is Latin for “the thing has been judged.” It basically means that once you sue someone and obtain a result–win or lose–the matter is over and you can’t sue the same person again for the same harm. It’s like the civil equivalent of double jeopardy. The doctrine is designed to conserve judicial resources, deter multiple lawsuits, and promote reliance on judicial decisions. A party claiming that a suit is barred by res judicata must establish: (1) a previous final judgment on the merits; (2) an identity of the cause of action in both suits; and (3) an identity of parties or their privies in the two suits.
A recent example is provided by Nathan v. Takeda, in which the United States Court of Appeals for the Fourth Circuit affirmed the district court’s dismissal of a defamation claim based on res judicata grounds.
In an earlier case, Noah Nathan sued his employer, Takeda Pharmaceuticals America, for discrimination and retaliation under Title VII. After proceeding to judgment in that case, he filed a second suit, this time including several Takeda employees as defendants and changing his legal theory to defamation, conspiracy, and negligent supervision and retention. Nathan admitted the existence of a prior final judgment on the merits, but argued that his second case should have been allowed to proceed because the causes of action were different and different parties were involved.