The functionality doctrine is a rule in trademark law which states that functional product features cannot serve as a trademark. A product feature is considered functional if it is essential to the use or purpose of the product or if it affects the cost or quality of the product. For example, in Valu Engineering, Inc. v. Rexnord Corp., the court decided that certain conveyor belt shapes were functional due to their increased performance over alternative designs and were therefore not eligible to be considered a trademark.
The goal of the functionality doctrine is to prevent companies from inhibiting legitimate competition by allowing that company to control a useful product feature without going through the patent process.
[Last updated in January of 2023 by the Wex Definitions Team]