Allegations of product tampering can be among the most complex and challenging cases handled in forensic laboratories. The vast majority of reported product tampering is, in fact, nothing of the sort, leaving the analyst in the unenviable position of trying to prove a negative. Yet, in instances of real tampering, the adulteration can take an almost infinite variety of forms. Tampering is usually thought of as the addition of some deleterious material to a product, but can also be the removal of a desired material from the product, or substitution of an ingredient of inferior quality for a specified component. Any of these forms of tampering has the potential to cause injury or death, even if that is not the intent of the perpetrator. Furthermore, when tampering does happen, an added or substituted agent can be almost any chemical entity imaginable, meaning that a thorough and conscientious investigation may require the application of an incredible variety of analytical techniques, from basic wet chemical color tests to analysis using top of the line instrumentation. This talk will provide an overview of key issues and considerations in the chemical analysis of alleged product tampering incidents, and will illustrate those points with examples drawn from real casework submissions at the FBI Laboratory.