Non-joinder of a necessary party happens when someone who should legally be included in a suit — because the court cannot accord complete relief without them or their interests would be impaired or exposed to risk of inconsistent obligations — is left out of the case. In practice you deal with it by (1) identifying such parties early through a careful factual and title/interest review, (2) moving promptly to join or implead them (courts can order joinder and rules like FRCP 19 and Rule 21 provide procedures to add parties), and (3) if joinder is not feasible (e.g., sovereign immunity or jurisdictional limits), asking the court to apply the Rule 19(b) factors to decide whether the case must be dismissed or can proceed without the absent party. Best practices from experienced litigators include doing thorough early-party due diligence, pleading alternative theories (so relief can be granted even if a party is later added), raising or defending non-joinder issues promptly (don’t wait until trial), considering alternatives like interpleader/impleader or contribution claims, and preparing to show how prejudice can be avoided if a party remains absent — these steps reduce the risk of costly dismissal or retrial.
