A Practice Note discussing the fundamentals of making and substantiating advertising claims. This Note focuses on the broad categories of claims, such as express, implied, monadic, and comparative claims. It discusses common categories of claims, common specific claims, and the substantiation needed to support them, such as environmental benefit (green) claims, pricing claims, market share claims, US origin claims, and various health-related food claims. It also discusses the difference between claims and puffery.