4. The Federal Rules authorize the joinder of multiple parties and multiple claims in a single lawsuit. See Chapter 9, infra. Many joinder variations are possible. For example, a single plaintiff may wish to file multiple claims against a single defendant, or multiple plaintiffs may wish to file multiple claims against a single defendant, and so forth. Courts have developed a number of rules, referred to as rules of aggregation, for determining when the amount-in-controversy requirement is met in the complex situations that typically arise.

See Gensler, Diversity Class Actions, Common Relief, and the Rule of Individual Valuation, 82 Ore. L. Rev. 295 (2003).