Some Confederate armies were named for the general areas of states in which they operated. Thus, the Army of Tennessee, which was organized by General Braxton Bragg while fighting in Tennessee, and the Army of Northern Virginia, which saw the bulk of its fighting in the northern part of Virginia, serve as examples.

The Army of Northern Virginia (ANV) was organized into two Corps until after the Battle of Chancellorsville in May of 1863. The First Corps was led by Lieutenant General James Longstreet ("Lee's Old Warhorse"), while the Second Corps was commanded by Lieutenant General Thomas Jonathan Jackson ("Stonewall"). Jackson was killed at Chancellorsville, succumbing to pneumonia after being wounded in a friendly fire incident.

Planning for the invasion of Pennsylvania, which was to become the Gettysburg Campaign, was started in late 1862, shortly after the Battle of Fredericksburg. Jackson ordered his mapmaker, Jedediah Hotchkiss, to construct a map of the area from the lower Shenandoah Valley across the Potomac River into the Cumberland Valley to Harrisburg, Pennsylvania, thence east to Baltimore. Hotchkiss constructed a map using 1850 and 1860 census maps, and other maps issued by the various counties in Virginia, Maryland, and Pennsylvania. The entire map, when completed, was about the size of a door. On it were the locations of nearly all the rural buildings in the area, complete with the names of their owners, and the construction materials used for the buildings and types of fences. The detail is amazing.

Lee, and Confederate President Jefferson Finis Davis, and other Confederate leaders were at odds about what to do strategically in 1863. There were calls to send Longstreet's Corps west to relieve the siege of Vicksburg, but Lee felt it of paramount importance to retain his Army of Northern Virginia, and help Vicksburg by invading the North. It would also give the beleaguered farmers of the Shenandoah Valley (the Confederacy's breadbasket) and northern Virginia a chance to get their crops planted, and allow them time to grow. With luck, a sustained invasion would last until the crops could be harvested, or until the victorious ANV marched on Baltimore and Washington, having defeated its Union counterpart, the Army of the Potomac.

Lee's strategic plan was approved. But, before he could move his forces north, he had to deal with the loss of Jackson. Accordingly, he promoted two able and senior division commanders to corps command, and by reassigning several brigades and divisions, split his army into three corps. The First was still commanded by Lieutenant General Longstreet, and contained three divisions under Major Generals George E. Pickett, Lafayette McLaws, and John Bell Hood. Second Corps was commanded by Lieutenant General Richard Stoddert Ewell, and contained the divisions of Major Generals Robert E. Rodes, Jubal Anderson Early, and Edward Johnson. Third Corps was commanded by Lieutenant General Ambrose Powell Hill. A. P. Hill's corps contained three divisions, commanded by Major Generals Henry Heth, William Dorsey Pender, and Richard Herron Anderson. (Please visit "The Generals" section on the "South" side for a complete "Order of Battle" of the Army of Northern Virginia.) Each Infantry division contained three to five brigades, each of which contained four to six regiments, usually from a single state. The brigades were known by the names of the Brigadiers (and sometimes Colonels) commanding them, but the regiments were designated numerically. Each regiment contained approximately 200-500 men. The entire Army of Northern Virginia at Gettysburg contained approximately 70,000-80,000 men.

Each infantry division also contained an artillery battalion, comprised of (usually) four batteries, each containing (usually) two sections of two guns, bringing the (usual) battalion total to 16 guns. Cannons varied in type and size, from 8 and 10 pounder Parrots, to Napoleons, Howitzers, and other types, on up to 20 pounder heavy artillery. In addition, each corps contained an artillery reserve force comprised of 2 battalions.

The Cavalry Division, under Major General James Ewell Brown Stuart (J.E.B. Stuart) contained six brigades under the command of Brigadier Generals Wade Hampton, Fitzhugh Lee, Albert Gallatin Jenkins, Beverly H. Robertson, William E. Jones, and Colonel J. R. Chambliss. Stuart's Division also contained a battalion of "Horse Artillery" under Major R. F. Beckham. Jenkins and a seventh brigade, under Brigadier General John D. Imboden, operated independently of Stuart at the start of the campaign, ranging the countryside around the main columns of the army (Longstreet and Hill), and even managing to throw some artillery shells at Mechanicsburg, across the river from the Pennsylvania Capital at Harrisburg.

Lee moved north in mid June from below the Potomac River, slowly sending his troops up the Shenandoah Valley and its northern extension, the Cumberland Valley, while sending Ewell's Corps east to seize and hold key points such as the bridges over the Susquehanna River at Harrisburg, and at Wrightsville between York and Lancaster Counties. Jubal Early's division seized York after having marched through Gettysburg in late June, and but for the work of some local militia, would have captured the Wrightsville-Columbia Bridge. The retreating militia fired the mile-long bridge as they withdrew from the western side of the river.

Other Union militia units, including some cavalry, operated in and around the Gettysburg area, notably west of town, "feeling" for the enemy. When they encountered forces of the ANV, the militia, lightly trained and equipped, and usually poorly led, would manage to "skedaddle", or in many cases become captives of the Southern troops.

On June 30, one of Lieutenant General A. P. Hill's brigades, under the command of Brigadier General James Johnston Pettigrew, marched east from South Mountain, toward Gettysburg in a vain search for boots and shoes. Approaching Gettysburg, Pettigrew, an accomplished soldier, saw the advanced elements of Union Brigadier General John Buford's First Division of the Cavalry Corps of the Army of the Potomac. (Please see "The Generals" and "The Army" sections on the "North" side.) Recognizing them as full army units, and not militia, an alarmed Pettigrew canceled the search for shoes and withdrew back to the foothills of South Mountain. There he reported his findings to Lieutenant General A. P. Hill, and to General Lee. Neither man credited the reported troops as anything other than militia. Hill, with the permission of Lee, ordered one of his other division commanders, Major General Henry Heth, to advance his division to Gettysburg the next morning, thus starting the concentration of his widely spread forces into the Gettysburg area. While Ewell ordered his three divisions to Gettysburg, and Hill ordered the rest of his men to follow Heth, Longstreet's men were still in the Cumberland Valley around Chambersburg. 

By about 8 AM on July 1, Heth's men were being fired upon by Buford's cavalry. The troopers were fighting dismounted on McPherson's Ridge, astride the Chambersburg Pike, northwest of Gettysburg. The battle was on.