The Bayern class was a class of four dreadnought battleships built for the German Kaiserliche Marine (Imperial Navy). The class comprised Bayern, Baden, Sachsen, and Württemberg. Construction started on the ships shortly before World War I; Baden was laid down in 1913, Bayern and Sachsen followed in 1914, and Württemberg, the final ship, was laid down in 1915. Only Baden and Bayern were completed, due to shipbuilding priorities changing as the war dragged on. It was determined that U-boats were more valuable to the war effort, and so work on new battleships was slowed and ultimately stopped altogether. As a result, Bayern and Baden were the last German battleships completed by the Kaiserliche Marine.

Bayern and Baden were commissioned into the fleet in July 1916 and March 1917, respectively. This was too late for either ship to take part in the Battle of Jutland on 31 May and 1 June 1916. Bayern was assigned to the naval force that drove the Imperial Russian Navy from the Gulf of Riga during Operation Albion in October 1917, though the ship was severely damaged by a mine and had to be withdrawn to Kiel for repairs. Baden replaced Friedrich der Grosse as the flagship of the High Seas Fleet, but saw no combat.

Both Bayern and Baden were interned at Scapa Flow following the Armistice in November 1918. Rear Admiral Ludwig von Reuter, the commander of the interned German fleet, ordered his ships be sunk on 21 June 1919; Bayern was successfully scuttled, though British guards managed to beach Baden to prevent her from sinking. The ship was expended as a gunnery target in 1921. Sachsen and Württemberg, both at various stages of completion when the war ended, were broken up for scrap metal. Bayern was raised in 1934 and broken up the following year.

Design work on the class began as early as 1910, with great consideration given to the armament of the new vessels. It had become clear that other navies were moving to guns larger than 30.5 cm (12 in), and so the next German battleship would also have to incorporate larger guns. The Weapons Department suggested a 32 cm (12.6 in) gun, but during a meeting on 11 May 1910, Admiral Alfred von Tirpitz, the State Secretary of the Reichsmarineamt (Imperial Naval Office), decided that budgetary constraints precluded the adoption of larger weapons. The following year, in the aftermath of the Agadir Crisis, Tirpitz quickly seized on public outcry over the British involvement in the crisis to pressure the Reichstag (Imperial Diet) into appropriating additional funds for the Navy. This provided the opening for more powerful battleships, so Tirpitz requested funds for ships armed with 34 cm (13.4 in) guns in mid-1911.

In August that year, the design staff prepared studies for ships armed with 35 cm (13.8 in), 38 cm (15 in), and 40 cm (15.7 in) guns; the 40 cm caliber was set as the maximum, since it was (incorrectly) assumed that British wire-wound guns larger than that could not be built. During a meeting the following month, the preferred designs were a ship armed with ten 35 cm guns in five turrets or eight 40 cm guns in four turrets. The Weapons Department advocated the 35 cm gun ship, pointing out that it would have a 25% greater chance of hitting its target. Tirpitz inquired about a mixed battery of twin and triple turrets, but after examining the gun turrets of the Austro-Hungarian dreadnoughts of the Tegetthoff class, it was determined that the triple gun turrets still had too many problems. Among these deficiencies were increased weight, reduced ammunition supply and rate of fire, and loss of fighting capability if one of the turrets was disabled.

Design studies suggested that the 35 cm ship would displace around 29,000 t (28,540 long tons; 31,970 short tons) and cost around 59.7 million marks, while the 40 cm proposal would cost approximately 60 million marks and displace 28,250 t (27,800 long tons), but both of these ships were deemed to be too expensive. The Construction Department proposed a 28,100 t (27,700 long tons) ship armed with eight 38 cm guns, which reduced the cost to 57.5 million marks per vessel. This design was adopted as the basis for the next class of battleship on 26 September, and the decision to adopt the 38 cm gun was formally taken on 6 January 1912. Work continued on the design into 1912, and included further developing the armor layout that had been adopted in the previous König class. The ships were originally projected to be armed with eight 8.8 cm (3.5 in) anti-aircraft guns, though they were not completed with any. Since the development of diesel engines was proving to be problematic, the design staff adopted traditional steam turbines for the ships, though it was hoped that by the time the third member of the class was ready to begin construction, reliable diesel engines would be available.

Funding for the vessels was allocated under the fourth Naval Law, which was passed in 1912. The Fourth Naval Law secured funding for three new dreadnoughts, two light cruisers, and an increase of an additional 15,000 officers and men in the ranks of the Navy for 1912. The capital ships laid down in 1912 were the Derfflinger-class battlecruisers; funding for Bayern and Baden was allocated the following year. Funding for Sachsen was allocated in the 1914 budget, while Württemberg was funded in the War Estimates. The last remaining Brandenburg-class pre-dreadnought, Wörth, was to be replaced, as well as two elderly Kaiser Friedrich III-class pre-dreadnoughts, Kaiser Wilhelm II and Kaiser Friedrich III. Baden was ordered as Ersatz Wörth, Württemberg as Ersatz Kaiser Wilhelm II, and Sachsen as Ersatz Kaiser Friedrich III; Bayern was regarded as an addition to the fleet, and was ordered under the provisional name "T".

Bayern and Baden were 179.4 m (588 ft 7 in) long at the waterline, and an even 180 m (590 ft 7 in) long overall. Sachsen and Württemberg were slightly longer: 181.8 m (596 ft 5 in) at the waterline and 182.4 m (598 ft 5 in) overall. All four ships had a beam of 30 m (98 ft 5 in), and had a draft of between 9.3 and 9.4 m (30 ft 6 in and 30 ft 10 in). Bayern and Baden were designed to displace 28,530 t (28,080 long tons; 31,450 short tons) at a normal displacement; at full combat load, the ships displaced up to 32,200 t (31,700 long tons; 35,500 short tons). Württemberg and Sachsen were slightly heavier, at 28,800 t normal and 32,500 t fully laden. The ships were constructed with transverse and longitudinal steel frames, over which the outer hull plates were riveted. The hull was divided into 17 watertight compartments, and included a double bottom that ran for 88 percent of the length of the hull.