The formation of the Energetic Materials Group focused on many issues involving the science and engineering of energetic materials. One unresolved issue is the meaning of “energetic materials.” This paper attempts to identify a rational for defining the category of Energetic Materials. The paper will first review the categories of energetic materials identified in the literature, addressing the advantages and disadvantages of each. Based upon the results of the analysis, a concise definition of Energetic Materials will be proposed.