Brown v. Felsen is a significant U.S. Supreme Court case from 1981 that addresses the principles of claim preclusion, also known as res judicata. This case established that a debtor's discharge in bankruptcy does not necessarily preclude litigation in a subsequent civil action regarding issues that could have been raised in the bankruptcy proceedings. It highlighted the importance of distinguishing between matters that are actually litigated and those that are merely relevant to a judgment, reinforcing how claim preclusion applies in bankruptcy contexts.