This chapter covers the basics of the chemistry of volatile organic compounds (VOCs) and what may make up the chemical profile of the odor of human remains, all for the purpose of helping one understand the complexities that a human remains detector (HRD) canine faces when deployed. How different types of tissues and compounds break down (including proteins, carbohydrates, and fats) is covered to give the reader a high-level understanding of the odors that may be created in certain situations and environmental conditions. A discussion of different types of training aids that may be used for training and maintaining an HRD canine is covered and some of the advantages and/or disadvantages of each. Finally, summaries of some of the research conducted regarding VOCs identified in different environmental conditions are provided.