This thesis examines the effect the rifle had on infantry tactics during the Civil War. It traces the transition from smoothbore to rifle and the development of the Minie ball. The range and accuracy of various weapons are discussed and several tables illustrate the increased capabilities of the rifle. Tactics to exploit the new weapon are examined, primarily those of William Hardee. Using Hardee’s tactics as the standard rifle tactics before the war, the change in how infantry soldiers fought is documented with two battle analyses. The 1862 Maryland Campaign shows the start of tactical evolution as soldiers seek cover, expend large quantities of ammunition and are decisively engaged at greater distances. During the 1864 Wilderness-Spotsylvania battle, the concepts of fortification defense and skirmish offense take hold. Examining several current books that deal with the rifle and its effects, the thesis concludes that the rifle’s increased firepower was a major factor in the move away from Hardee’s formation tactics.