This research guide is an introduction to military intelligence, a neglected aspect of warfare that provides commanders and national leaders with essential information for decision making. The introduction provides the general reader with an explanation of the terminology, procedures, and institutional problems of military intelligence, while outlining the history of this field and identifying areas for further research. The core of the guide is an extensively annotated bibliography of unclassified English language materials on military intelligence, the evolution of intelligence operations, the role of intelligence in air, ground, and naval operations, and specialized fields of espionage, counter intelligence, technical intelligence, and aerial photography. This guide is intended to fill a void in the literature for soldiers, historians, and general readers.