The Republic of Korea Navy (ROKN; Korean: 대한민국 해군), also known as the ROK Navy is the naval warfare service branch of the South Korean armed forces, responsible for naval and amphibious operations. The South Korean navy includes the Republic of Korea Marine Corps, which functions as a branch of the Navy. The ROK Navy has about 80,000 regular personnel including 30,000 Republic of Korea Marines. There are about 262 commissioned ships in the ROK Navy. The naval aviation force consists of about 88 fixed-wing and rotary-wing aircraft. The ROK Marine Corps has about 300 tracked vehicles including assault amphibious vehicles.

The Republic of Korea Navy was established as the Marine Defense Group on November 11, 1945, after Korea was liberated from the Empire of Japan on August 15, 1945. Since the Korean War, the South Korean navy had concentrated its efforts on building naval forces to counteract hostilities of North Korea. As South Korea's economy grew, the ROK Navy was able to locally build larger and better equipped fleets to deter aggression, to protect the sea lines of communication, and to support the nation's foreign policy. As part of its mission, the ROK Navy has engaged in several peacekeeping operations since the turn of the 21st century. The ROK Navy aims to become a blue-water navy in the 2020s.

The main duties of the Navy shall be operations on the sea, including landing operations, and the main duties of the Marine Corps shall be landing operations, and the Navy and Marine Corps shall be formed and equipped for that purpose and shall provide education and training necessary therefor.

— Act on the Organization of National Armed Forces

The objectives of the ROK Navy as the main force for the national security and prosperity are:

Korea has a long history of naval activity. In the late 4th century during the Three Kingdoms period, Goguryeo defeated Baekje, fielding amphibious forces of 40,000 men in the process. In 732, the Balhae navy "attacked the Shandong peninsula and destroyed the biggest seaport of the Tang Empire in the east – Dengzhou." In the 9th century, Commissioner Chang Pogo of Unified Silla established a maritime base called Cheonghaejin on an island to foster trading with China and Japan, and to eradicate pirates.

In 1380, naval forces of the Goryeo dynasty defeated 500 invading Japanese pirate vessels by deploying shipboard guns, devised by Ch'oe Mu-sŏn. This is reportedly the first use of shipboard guns in naval history. In 1389 and 1419, Korean naval forces invaded Tsushima Island to suppress Japanese piracy. In the early years of the Joseon dynasty, the naval force reached its peak of 50,000 personnel, in order to combat the ongoing piracy issue.

During the Japanese invasions of Korea (the Imjin War) in the 16th century, the Korean naval force commanded by Admiral Yi Sun-sin, who later became the head of the navy, cut off the invaders' naval lifeline and defeated the Japanese fleet, reversing the war in favor of Joseon. Admiral Yi is also credited with the creation of the Turtle Ship.