Canines are sensitive and selective, non-contact vapor detectors that can easily be trained to locate novel materials; however, unlike other vapor detection instrumentation or sensors, canines do not give a readable output, thus leaving the handler to interpret canine behavior. One way to better understand canine response to odor and ultimately better the detector is to improve the understanding of factors that affect or change odor. A compilation of research will be discussed that describes odor on a molecular level as it relates to detection of a target. This will include the basics of odor chemistry, how odor emanates from a target object and how the dog might perceive this odor. These fundamental topics will be applicable to all detection discplins; however, examples and case studies from studies relating to the detection of explosives, drug (fentanyl), human remains, and sport detection will be used.