This is a web-based lesson on the principles of rational prescribing. It includes three cases and addresses polypharmacy, adverse drug events, and off-label prescribing. The principles apply to all patient populations, but this lesson focuses on older adults because they constitute a large and growing population at high risk of polypharmacy and unwanted side effects of medications. The lesson utilizes PowerPoint slides, audio, and interactive features including focus questions within the cases and a specially created drug interaction game. Printable resources available for download include the American Geriatrics Society's Beers Criteria Pocket Card and a sample medication grid for patient use. The lesson is free and requires about 15 minutes to complete.