Under what condition can multiple defendants be joined in a single federal lawsuit?

Joinder of multiple defendants in a single federal lawsuit is permissible when the claims against them arise from the same transaction or occurrence. This principle promotes judicial efficiency by allowing all related issues to be resolved in one lawsuit, thereby avoiding the potential for inconsistent judgments and reducing the burden on the court system.

The focus on a common transaction or occurrence ensures that the claims are sufficiently interconnected, justifying their consolidation. This means that the factual and legal underpinnings of the claims share a significant relationship, which can facilitate a clearer and more organized judicial process.

In contrast, options that involve unrelated defendants presenting only a unified defense, scenarios involving a federal question without a direct connection among the claims, or merely sharing legal representation do not meet the necessary criteria for proper joinder under the rules governing civil procedure. Thus, the requirement for a connection through the same transaction or occurrence is essential for effective joinder.