Major concepts usually applicable to evidence in sexual assault cases are evidence identification, class characteristic evidence, individual characteristic evidence, evidence transfer, evidence environment, and evidence contamination. Evidence identification involves distinguishing between class characteristic evidence, which cannot be forensically identified with a specific source to the exclusion of all others, and individual characteristic evidence, which can be positively identified with a specific source to the exclusion of all others. Evidence transfer involves the movement of evidence from one person or place to another. Evidence environment refers to the mingling of different types of material in identifiable combinations to produce a unique condition. Although evidence may be contaminated before it is discovered, evidence processors must halt or limit further contamination. The victim, suspect, and crime scene are the major sources of evidence in sexual assault cases. In discussing these sources, this paper focuses on the kinds of evidence that might be collected from such sources, the procedures required to obtain evidence and ensure its integrity and chain of custody (e.g., sexual assault evidence collection kit), and specialized techniques that can enhance the discovery of small amounts of evidence.