Tiny fragments of physical evidence such as hairs, fibers from clothing or carpeting, or pieces of glass are examples of trace evidence, and can be transferred when two objects touch or when small particles are disbursed by an action or movement. This evidence can be used to reconstruct an event or indicate that a person or thing was present. Careful collection of materials from a crime scene can yield a wealth of information about where a sample came from and how it helps to tell the story. This guide explains the principles of trace evidence, how and when trace evidence is used, common terms and other resources about trace evidence.