An indispensable party is a party in a lawsuit whose participation is required for jurisdiction or the purpose of rendering a judgment. An indispensable party may usually be joined at the discretion of the judge. Often, an indispensable party is any party whose rights are directly affected by disposition of the case.

The indispensable party is often a prudential standing requirement. That is, while the parties currently involved in litigation have an actual case or controversy, judges will not proceed without the indispensable party. This avoids potential double litigation and possibly inequitable outcomes.

In patent law, a patent owner must be a party to a patent infringement suit by an exclusive licensee because the patent owner's rights would be directly affected by a finding of invalidity or unenforceability of the patent claims.