无畏舰（英语：Dreadnought）是一种活跃于二十世纪初期的战舰类型。1906年，英国皇家海军的「无畏号」下水服役，由于其技术与设计之先进远超过同时代的战舰，故以其为名自成一种新型战舰的类别——「无畏舰」，而落伍的旧式战舰则全部被归为「前无畏舰」，意旨「无畏舰」出现前设计者。

「无畏舰」具两种革命性的创新设计，一为采取「全重砲」武装配置，其装备的大口径火砲数远超过以往的战舰，二为使用蒸汽涡轮发动机作为推进系统。随着「无畏舰」逐渐成为海上力量、乃至于国力的重要指标，各国展开了规模巨大的「无畏舰」建造竞赛，遍及欧洲、亚洲和美洲国家，尤其是英国与德国最为激烈、建造数量最多。「无畏舰」造舰竞赛一定程度上促成了第一次世界大战的爆发，并一直持续到开战当年，在仅仅五年造舰技术迅速发展的时间里，「无畏舰」在火砲口径、吨位、装甲和推进力都有了飞跃性的提高，甚至出现了在前述的技术指标上发展到极致的「超无畏舰」，而原先领先全球的「无畏号」反而在开战后成了落伍的二线战舰。一次大战结束后，世界海军列强为避免再因造舰竞赛重起战端，召开了「华盛顿裁军会议」，以此限制各国海军军舰的吨位和武装，但许多艘「超无畏舰」依旧服役到第二次世界大战。

The dreadnought was the predominant type of battleship in the early 20th century. The first of its kind, the Royal Navy's Dreadnought, made such a strong impression on people's minds when launched in 1906 that similar battleships built subsequently were referred to generically as "dreadnoughts", and earlier battleships became known as "pre-dreadnoughts". Dreadnought's design had two revolutionary features: an "all-big-gun" armament scheme, with more heavy-calibre guns than previous ships, and steam turbine propulsion. As dreadnoughts became a crucial symbol of national power, the arrival of these new warships was a crucial catalyst in the intensifying naval arms race between the United Kingdom and Germany. With the launch of a single ship, Dreadnought, the scales of naval power were reset overnight. As a result, dreadnought races sprang up around the world, including in South America, during the lead 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 had outclassed Dreadnought. 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 to be used throughout World War II. The only surviving dreadnought is USS Texas, located near the San Jacinto Battleground State Historic Site.