This book will discuss the effects of infectious disease on Napoleon's forces during the Russian campaign of 1812. In short, it will argue that the primary reason Napoleon failed to defeat the Russian army was because his forces were decimated by disease, specifically typhus, dysentery, and diphtheria. It will also demonstrate the affect of disease and illness on Napoleon's judgement and decision making process. This subject, infectious disease and the military, has great implications for military planners in the future. The recent Gulf war and its related "Gulf War Illness" is just one example. The United States has lost more men to disease during war than any other cause, hence it is critical that today's and tomorrow's military leaders are aware of the dangers. The scope of this book is bounded by the Russian campaign timeframe, but it will concentrate on the march to Moscow; specifically the events that occurred upon entering Polish and Russian territory. Also, there were two major battles fought prior to reaching the gates of Moscow which this work will show were the two decisive points in the campaign. These battles occurred at Smolensk and Borodino, and they illustrate key instances where Napoleon's leadership, judgment and decision making come into question, not only by historians and authors, but by several of Napoleon's own generals. The book will be broken down into three main chapters; chapter one will include the introduction and describe the three main infectious disease threats, and an estimate of the composition of forces that Napoleon started with so as to show the numbers of men killed or incapacitated by disease, and a short discussion on hospital/medical facilities. Chapter two will emphasize the period of time between the French forces entering Poland and first encountering the deadly typhus, to when the remaining army reached Moscow. It will give accounts of Napoleon's actions at Smolensk and Borodino and will outline the losses caused by disease. Specifically, it will show that Napoleon himself was weakened by sickness and this affected his judgement and his ability to conduct the campaign in a successful manner. He failed to press the advantage at Borodino even after repeated attempts by his Generals to convince him to commit his Imperial Guard to defeat the almost beaten Russians. Borodino, it could be argued, was the first Waterloo for Napoleon. After that battle, he would never again reach the strength he then possessed. Chapter three will discuss the events leading to the occupation of Moscow and the French departure. It will also discuss Russian strategy, and the applicability of infectious disease to today's military leaders. The Russians were outnumbered in the summer of 1812 and were forced to play at fight and retreat game with Napoleon's army. This was not well received by the Russian people who were suffering at the hands of the French invaders, but it was just about the only sound course of action the Russians could pursue. The situation turned itself around however when Napoleon reached Moscow and stayed there until an orderly and safe retreat was nearly impossible. At this time the Russian winter was upon them and they had neither the will nor the supplies to return to France. The effects of disease upon Napoleon and his Army were too much even for the great General to overcome. He could not foresee the decimation, but he could have altered his plans after it began to take hold of his army.