This document provides information on gear tooth wear and damage. The material contained herein is intended to help the user better understand damage to gear teeth, but the potential reasons for damage and preventive measures discussed are not definitive. Also, for individual cases, other reasons for damage or measures can exist that are not mentioned in this document. At the same time, reasons for damage or measures mentioned in this document are not always of importance. In many cases, damage can be the result of multiple interacting factors. Some causes that are included are still a topic of research and discussion but are presented with the intent to provide possibilities. The solution to many gear problems involves detailed investigation and analysis by specialists; this document is not intended to replace such expert knowledge.