Trace evidence can provide powerful evidentiary value for the investigation of either criminal or civil cases if it is documented, collected and examined properly. Trace evidence consists of a variety of materials that occur in a variety of forms and often in small sizes. Thus, a variety of methods are available for their collection both in the field and at the laboratory. Proper collection needs to be conducted on both unknown specimens and known samples, particularly when comparative examinations are requested. Collecting evidence is not only confined to a technical operation of correctly using devices or tools for collection. An informed selection is required from the part of the crime scene investigator or the trace evidence examiner at the laboratory. The selection step is based on judgments of the relevancy of observed traces or of objects supposed to be related to the case at hand. The term of material clues is used in this chapter to qualify traces recognized to be pertinent in the light of the context of the case. It is also acknowledged that traces shed on a given surface or taken away from a surface may not be immediately detected. This is especially true for microscopic debris of all sorts. Their presence can only be hypothesized during the collection step and be verified by thorough microscopical search at the laboratory. The concepts of targeted and non-targeted approaches are discussed to distinguish these aspects. The general principles and techniques for trace evidence collection are discussed in this chapter in order to properly utilize, manage and value trace evidence for criminal and civil investigations.