The central issue in any trademark infringement action is whether the defendant's mark is likely to cause consumer confusion regarding sponsorship, affiliation, or connection between the parties or their goods or services. This Toolkit provides continuously maintained resources designed to provide guidance on the law governing the likelihood of confusion test and analysis.

The Toolkit includes checklists setting out the likelihood of confusion law in each circuit except for the D.C. Circuit. The US Court of Appeals for the D.C. Circuit has not decided many trademark infringement cases and the law is not well-developed in the circuit. District courts in the D.C. Circuit therefore often cite to the appellate court decisions in other circuits.