Most crime scene examiners are aware of the Locard exchange principle, usually captured in the phrase, “Every contact leaves a trace.” Setting aside the fact that Locard never actually said that, although it is implied in his writings, the principle has had negative as well as positive consequences in forensic science. On the positive side, it is a reminder that the purpose of much of forensic science is to investigate associations between people and places and people with other people, as part of testing the hypotheses formulated around events at the scene. On the negative side, issues of loss, redistribution, contamination, and lack of reference statistical databases, as well as many questions regarding the integrity of conclusions based on comparison of often limited and ill-defined properties of materials rather than on showing their identity, have led to less and less reliance being placed on the time-consuming and subjective examination of traditional forms of trace evidence.