This module covers the foundation of DNA evidence: defining, recognizing, collecting, and testing. The module begins by describing the process of visual examination and chemical screening at the scene to establish the presence of biological material. Then, the module defines DNA and presents the scientific basis for DNA testing as a means to establish the donor of a specific biological sample. How to collect that genetic material and its various substrates is then explained. Finally, the module concludes with a discussion of how DNA samples are processed and tested.