The Panther tank, officially Panzerkampfwagen V Panther (abbreviated Pz.Kpfw. V) with ordnance inventory designation: Sd.Kfz. 171, is a German medium tank of World War II. It was used in most European theatres of World War II from mid-1943 to the end of the war in May 1945.

The Panther was intended to counter the Soviet T-34 medium tank and to replace the Panzer III and Panzer IV. Nevertheless, it served alongside the Panzer IV and the heavier Tiger I until the end of the war. While having essentially the same Maybach V12 petrol (690 hp) engine as the Tiger I, the Panther had better gun penetration, was lighter and faster, and could traverse rough terrain better than the Tiger I. The trade-off was weaker side armour, which made it vulnerable to flanking fire, and a weaker high explosive shell. The Panther proved to be effective in open country and long-range engagements. The Panther had excellent firepower, protection and mobility, though early variants suffered from reliability issues. The Panther was far cheaper to produce than the Tiger I. Key elements of the Panther design, such as its armour, transmission, and final drive, were simplifications made to improve production rates and address raw material shortages.

The Panther was rushed into combat at the Battle of Kursk in the summer of 1943 despite numerous unresolved technical problems, leading to high losses due to mechanical failures. Most design flaws were rectified by late 1943 and early 1944, though the Allied bombing of production plants in Germany, increasing shortages of high-quality alloys for critical components, shortage of fuel and training space, and the declining quality of crews all impacted the tank's effectiveness. Though officially classified as a medium tank, at 44.8 metric tons the Panther was closer in weight to contemporary foreign heavy tanks. The Panther's weight caused logistical problems, such as an inability to cross certain bridges; otherwise, the tank had a very high power-to-weight ratio which made it highly mobile.

The naming of Panther production variants did not follow alphabetical order, unlike most German tanks – the initial variant, Panther "D" (Ausf. D), was followed by "A" and "G" variants.

The Panther was born out of a project started in 1938 to replace the Panzer III and Panzer IV tanks. The initial requirements of the VK 20 series called for a fully tracked vehicle weighing 20 tonnes and design proposals by Krupp, Daimler-Benz and MAN ensued. These designs were abandoned and Krupp dropped out of the competition entirely as the requirements increased to a vehicle weighing 30 tonnes, a direct reaction to the encounters with the Soviet T-34 and KV-1 tanks and against the advice of Wa Prüf 6. The T-34 outclassed the existing models of the Panzer III and IV in certain metrics, such as effective armour thickness and gun caliber. At the insistence of General Heinz Guderian, a special tank commission was created to assess the T-34. Among the features of the Soviet tank considered most significant was the sloped armour, which gave much improved effective armour thickness, the wide track, which improved mobility over soft terrain, and the 76.2 mm (3 in) gun, which had good armour penetration and fired an effective high-explosive round. Daimler-Benz (DB), which designed the successful Panzer III and StuG III, and Maschinenfabrik Augsburg-Nürnberg AG (MAN) were given the task of designing a new 30- to 35-tonne tank, designated VK 30.02, by April 1942.

The VK 30.02(DB) design resembled the T-34 in its hull and turret and was also to be powered by a diesel engine. It was driven from the rear drive sprocket with the turret situated forward. The incorporation of a diesel engine promised increased operational range, reduced flammability and allowed for better use of petroleum reserves. Adolf Hitler considered a diesel engine imperative for the new tank. DB's proposal used an external leaf spring suspension, in contrast to the MAN's proposal of twin torsion bars. Wa Prüf 6's opinion was that the leaf spring suspension was a disadvantage and that using torsion bars would allow greater internal hull width. It also opposed the rear drive because of the potential for track fouling. Daimler-Benz still preferred the leaf springs over a torsion bar suspension as it resulted in a silhouette about 200 mm (7.9 in) shorter and rendered complex shock absorbers unnecessary. The employment of a rear drive provided additional crew space and also allowed for a better slope on the front hull, which was considered important in preventing penetration by armour-piercing shells.

The MAN design embodied a more conventional configuration, with the transmission and drive sprocket in the front and a centrally mounted turret. It had a petrol engine and eight torsion bar suspension axles per side. Because of the torsion bar suspension and the drive shaft running under the turret basket, the MAN Panther was higher and had a wider hull than the DB design. The Henschel company's design concepts for their Tiger I tank's suspension/drive components, using its characteristic Schachtellaufwerk format – large, overlapping, interleaved road wheels with a "slack-track" using no return rollers for the upper run of track, also features shared with almost all German military half-track designs since the late 1930s – were repeated with the MAN design for the Panther. These multiple large, rubber-rimmed steel wheels distributed ground pressure more evenly across the track. The MAN proposal also complemented Rheinmetall's already designed turret modified from that of the VK 45.01 (H), and used a virtually identical Maybach V12 engine to the Tiger I heavy tank's Maybach HL230 powerplant model.

The two designs were reviewed from January to March 1942. Reichsminister Fritz Todt, and later his replacement Albert Speer, both recommended the DB design to Hitler because of its advantages over the initial MAN design. At the final submission, MAN refined its design, having learned from the DB proposal apparently through a leak by a former employee in the Wa Prüf 6, senior engineer Heinrich Ernst Kniepkamp and others. On 5 March 1942, Albert Speer reported that Hitler considered the Daimler-Benz design to be superior to MAN's design. A review by a special commission appointed by Hitler in May 1942 selected the MAN design. Hitler approved this decision after reviewing it overnight. One of the principal reasons given for this decision was that the MAN design used an existing turret designed by Rheinmetall-Borsig, while the DB design would have required a brand new turret and engine to be designed and produced, delaying the commencement of production. This time-saving measure compromised the subsequent development of the design.