According to the Manual for Complex Litigation promulgated by the Federal Judicial Center, “Complex Litigation” is not “susceptible to any bright-line definition.” Some characteristics of complex litigation, however, are generally noticeable, and certain types of cases are generally deemed “complex” cases. Classic examples of "complex" cases include class actions, mass torts, securities cases, environmental pollution matters, antitrust cases, etc.
Characteristics typically found in “complex litigation” include:
- Multiple Parties. “Complex” lawsuits generally involve a large number of parties, such as found in class actions. Having a greater number of parties, however, doesn’t necessarily cause wasteful complexity. In fact, a multiplicity of parties usually results from the parties’ ability and willingness to afford the expense of complexity. But multiplying the number of parties can promote inefficiency and cause confusion for a number of reasons. For example, if the parties fall into disparate groups that have conflicting interests, it makes settlement harder to broker and the trial more involved and unpredictable.
- Great Resources. Litigants who don’t have resources can’t afford to make lawsuits complex. A wealthy litigant can bear the cost of complexity and - especially when the other side is poorer ─ may have an incentive to create and exploit complexity. The opposite is also true. Complexity rarely develops between poor parties.
- High Stakes. The more each side has to gain or lose, the greater the impulse to overdiscover, to over-litigate, over-analyze and to over-work the case.
 Manual for Complex Litigation, 4th, at 1 (2004).
 In class actions, class counsel’s resources (rather than the class representatives) determines the affordability of complexity.