What is environmental history? In the words of Brian Allen Drake, it is "the study of the interactions between humans and nature across time." It includes, but is in no way limited to, the study of the environment. Generally speaking, it is a way to interpret nature as an integral part of the past, as an important "actor." Or, to use an academic buzz term, environmental history "gives voice" to flora, fauna, weather, climate, geography, terrain, microbiology, and other non-human actors. A quick glance at any traditional history of the Civil War reveals that nature was omnipresent in the conflict. As one scholar playfully noted, the Civil War was, after all, "largely fought outdoors." Union and Confederate forces marched through forests and fields, occupied strategic positions atop hills and behind mountains and rivers, dug trenches and canals, confiscated and consumed crops, battled for control of waterways, trudged through rain and mud, contracted deadly diseases, torched enemy farms, cut and burned fences and trees, and depended on hogs, cattle, horses, and mules for sustenance and transportation. Like many of their nineteenth-century human subjects, most Civil War historians have depicted nature as something to be acted upon, dealt with, defeated, or overcome. Few have contemplated nature's pivotal role in shaping the conflict's course and outcome, and even fewer have explicitly investigated the ways in which Civil War soldiers used the environment to their strategic and tactical advantage. This article represents an attempt to convince history instructors to teach environmental history in their courses and, more precisely, in their classes on the Civil War. Specifically, the author proposes doing so through an examination of the 1863 Helena campaign. By examining three primary sources produced by soldiers who fought in the Helena campaign, students can discover the natural environment's central role in an important Civil War engagement. In the process, they also can learn how to do environmental history.