Trace evidence occurs when objects make contact, and material is transferred. This type of evidence is usually not visible to the naked eye and requires specific tools and techniques to be located and obtained. Due to this, trace evidence is often overlooked, and investigators must be trained to detect it. When it comes to an investigation trace evidence can come in many different forms and is found in a wide variety of cases. This evidence can link a victim to suspects and a victim or suspect to the crime scene.

There are three general categories in which forensic science uses trace evidence. It can be used for investigative aids, associative evidence, and in-scene reconstructions. In terms of investigative aids, trace evidence can provide information to determine the origin of a sample and determine the manufacture date of the material, all of which can limit potential suspects in a case. Associative evidence can associate with or link victims or suspects to a crime scene. For reconstructions, trace evidence can provide information to understand how a crime occurred or the events that occurred before the crime.

The importance of trace evidence in criminal investigations was shown by Edmond Locard in the early 20th century, with his exchange principle, that every contact leaves a trace. This statement can then be expanded by stating trace evidence must first be located and recorded before it can be recovered and analyzed. Since then, forensic scientists use trace evidence to reconstruct crimes and to describe the people, places, and things involved in them. Studies of homicides published in the forensic science literature show how trace evidence is used to solve crimes.

Trace evidence is found in many different forms with some examples including, but not limited, to fire debris, gunshot residue, glass fragments, and fibres. Each of these types of evidence will have a trained analyst in that specific field who will conduct the analysis on these items.

Some case examples of the use of trace evidence could include a Vehicular accident reconstruction which relies on marks such as tire impressions to estimate vehicle speed before and during an accident, as well as braking and impact forces. Fibres from clothing worn by a pedestrian found in the paint and/or road grime of a striking vehicle can be linked to the specific vehicle involved in a hit-and-run collision. "Witness marks" are also an important form of trace evidence, especially in engineering and may be critical in understanding how a product failed. A typical witness mark could be an impact depression which broke a product. It is especially useful if that mark can be linked to the product which made the impact such as a hammer or nail. Such marks are also commonly encountered in criminal cases and include bite marks, puncture marks, bullet holes, etc.

After the trace evidence has been located at a crime scene the next step is to record it. There are multiple ways of recording evidence and that is dependant on the type of evidence found. The first option is to videotape the crime scene. This can be done to provide perspective on the actual location of the evidence throughout the entire scene. The next step in recording the evidence would be still photographs. The images included should be photos of the evidence both with flash and without, the evidence with a ruler for size reference, and the evidence with its number in the photo.

As for the recovery of the evidence, samples may be collected by handpicking, tape lifts, combing, or removal of an entire object. Hand picking is straightforward, with the evidence being carefully picked up by hand or with forceps and placed in the proper packaging for that specific item.  Tape lifts are used when the item cannot be picked up by hand or with forceps. It involves the sticky side of tape being placed on the evidence and then carefully lifting and placing it either on a sheet of clear acetate or on its original packaging. Combing is used when trace evidence needs to be removed from a person who is either alive or deceased. A different comb should be used for each piece of evidence being removed and the combs and paper must be packaged separate from the evidence. The removal of an entire object occurs when the evidence simply can not be removed from this object. The collection method used is entirely based on what the evidence type is and the surface it is on. It is also important to note that great care must be taken to prevent contamination of the evidence with other substances (such as natural oil and sweat on the hand of the collector).

Trace Evidence is also found in much smaller amounts at crime scenes.