Aggregation—the ability to join parties or claims in a federal civil lawsuit—has usually been governed by subject matter jurisdiction, claim and issue preclusion, and the joinder rules. These doctrines have tended to favor aggregation for its efficiency, consistency, and predictability. Yet aggregation is suddenly under attack from a new threat, one that has little to do with aggregation directly: personal jurisdiction. In this Article, I chronicle how a recent restrictive turn in personal jurisdiction—seen in modern cases narrowing general jurisdiction and October Term 2016’s blockbuster case Bristol-Myers Squibb—threatens the salutary benefits of aggregation across a number of areas, including simple joinder of parties and claims, representative actions, and multidistrict litigation. I offer a solution for preserving aggregation’s advantages in the face of this trend in personal jurisdiction: authorize a broader scope of personal jurisdiction in federal court for multiparty and multiclaim cases. I defend such a regime as constitutional and consistent with the norms of both personal jurisdiction and aggregation.