The Nassau class was a group of four dreadnought battleships built for the German Kaiserliche Marine in the early 1900s. The class comprised Nassau, the lead ship, Rheinland, Posen, and Westfalen. All four ships were laid down in mid-1907, and completed by late 1910. Though commonly perceived as having been built in response to the British Dreadnought, their design traces its origin to 1903; they were in fact a response to Dreadnought's predecessors of the Lord Nelson class. The Nassaus adopted a main battery of twelve 28 cm (11 in) guns in six twin-gun turrets in an unusual hexagonal arrangement. Unlike many other dreadnoughts, the Nassau-class ships retained triple-expansion steam engines instead of more powerful steam turbines.

The dreadnought was the predominant type of battleship in the early 20th century. The first of the kind, the Royal Navy's HMS Dreadnought, had such an effect when launched in 1906 that similar battleships built after her were referred to as "dreadnoughts", and earlier battleships became known as pre-dreadnoughts. Her design had two revolutionary features: an "all-big-gun" armament scheme, with an unprecedented number of heavy-calibre guns, and steam turbine propulsion. As dreadnoughts became a crucial symbol of national power, the arrival of these new warships renewed the naval arms race between the United Kingdom and Germany. Dreadnought races sprang up around the world, including in South America, lasting up to the beginning of World War I. Successive designs increased rapidly in size and made use of improvements in armament, armour, and propulsion throughout the dreadnought era. Within five years, new battleships outclassed Dreadnought herself. These more powerful vessels were known as "super-dreadnoughts". Most of the original dreadnoughts were scrapped after the end of World War I under the terms of the Washington Naval Treaty, but many of the newer super-dreadnoughts continued serving throughout World War II.