Boyde v. California is a significant case decided by the U.S. Supreme Court in 1990 that focused on the rights of defendants in criminal cases, particularly concerning jury instructions and the deliberation process. The case examined whether a trial court's failure to provide specific jury instructions about considering mitigating evidence during the sentencing phase violated the defendant's constitutional rights. This ruling emphasizes the importance of clear jury instructions to ensure jurors properly evaluate all relevant evidence when making their decisions.