Legal Definitions - claim preclusion

Claim preclusion is a fundamental legal principle that prevents parties from re-litigating a lawsuit that has already been decided by a court. Once a court has issued a final judgment on a specific legal claim, the parties involved are generally barred from bringing that same claim, or any related claims that *could have been* brought in the original lawsuit, in a new court case. This rule ensures finality in legal disputes, promotes judicial efficiency, and prevents parties from repeatedly suing each other over the same underlying issue. It applies not only to arguments actually made and decided in the first case but also to all arguments that *could have been* made as part of that claim.

Here are some examples to illustrate claim preclusion:

• Example 1: Contract Dispute

  A small business owner sues a software developer for breach of contract, alleging that the custom software delivered was buggy and unusable. After a trial, the court rules in favor of the software developer, finding no breach of contract. Under claim preclusion, the business owner cannot later file a *new* lawsuit against the *same software developer*, arguing that the *same contract* was breached because the software was delivered three months late, even if that specific argument about lateness was not explicitly raised in the first trial. The initial lawsuit concerned the overall breach of that contract, and all potential arguments related to that breach should have been brought forward at that time.

• Example 2: Personal Injury Case

  A pedestrian is hit by a car and suffers a broken leg and significant emotional distress. They sue the driver for medical expenses and property damage to their phone. The court awards them compensation for these specific damages. Claim preclusion would prevent the pedestrian from filing a *second* lawsuit against the *same driver* a year later, seeking additional compensation for lost wages, ongoing physical therapy, or pain and suffering arising from the *same accident*. The initial lawsuit encompassed all claims for damages resulting from that particular incident, and all potential forms of compensation should have been sought in that first action.

• Example 3: Employment Termination

  An employee is fired and sues their former employer for wrongful termination, alleging that their dismissal was discriminatory based on their age. The court hears the case and ultimately rules against the employee. Due to claim preclusion, the employee cannot then file a *new* lawsuit against the *same employer*, arguing that the termination was also a breach of their employment contract, if that contract breach claim could have been raised in the initial wrongful termination lawsuit. The core claim was about the legality of the termination, and all legal theories supporting that claim should have been presented together in the first case.