A battleship is a large armored warship with a main battery consisting of heavy caliber guns. Battleships were larger, better armed and armored than cruisers and destroyers. As the largest armed ships in a fleet, battleships were used to attain command of the sea and represented the apex of a nation's naval power from the nineteenth century up until World War II. With the rise of air power and guided missiles, large guns were no longer deemed necessary to establish naval superiority, and as a result there are no battleships in active service today.

Battleship design evolved to incorporate and adapt technological advances to maintain an edge. The word battleship was coined around 1794 and is a contraction of the phrase line-of-battle ship, the dominant wooden warship during the Age of Sail. The term came into formal use in the late 1880s to describe a type of ironclad warship, now referred to as pre-dreadnought battleships. In 1906, the commissioning of HMS Dreadnought heralded a revolution in battleship design. Following battleship designs that were influenced by HMS Dreadnought were referred to as "dreadnoughts".

Battleships were a symbol of naval dominance and national might, and for decades the battleship was a major factor in both diplomacy and military strategy. The global arms race in battleship construction beginning in the late 19th century and exacerbated by Dreadnought was one of the causes of World War I, which saw a clash of large battle fleets at the Battle of Jutland. The Naval Treaties of the 1920s and 1930s limited the number of battleships but did not end the evolution of design. Both the Allies and the Axis Powers deployed battleships of old construction and new during World War II.

The value of the battleship has been questioned, even during the period of their prominence. The Battle of Tsushima (1905) was the only decisive clash between steel battleship fleets, and apart from the indecisive Battle of Jutland (1916), there were few great battleship clashes. Despite their great firepower and protection, battleships were increasingly vulnerable to much smaller, cheaper ordnance and craft: initially the torpedo and the naval mine, and later aircraft and the guided missile. The growing range of naval engagements led to the aircraft carrier replacing the battleship as the leading capital ship during World War II, with the last battleship to be launched being HMS Vanguard in 1944. Battleships were retained by the United States Navy into the Cold War only for fire support purposes. The last battleships were removed from the U.S. Naval Vessel Register in March 2006.