Seoul, officially the Seoul Special City, is the capital and largest metropolis of South Korea. A megacity with a population of over 10 million, it is the largest city proper in the OECD developed world. The Seoul National Capital Area is the world's second largest metropolitan area with over 25 million inhabitants, which includes the surrounding Incheon metropolis and Gyeonggi province. Almost a quarter of South Koreans live in Seoul along with over 275,000 international residents.

Located in the Han River, Seoul has been a major settlement for over 2,000 years, with its foundation dating back to 18 B.C. when Baekje, one of the Three Kingdoms of Korea, established its capital in what is now south-east Seoul. It continued as the capital of Korea during the Joseon Dynasty and the Korean Empire. The Seoul National Capital Area is home to four UNESCO World Heritage Sites: Changdeokgung, Hwaseong Fortress, Jongmyo Shrine and the Royal Tombs of the Joseon Dynasty. Seoul is the world's greenest major city, with over 27% of the city dedicated to public parks such as Namsan Park, home to the N Seoul Tower.

Today, Seoul is considered to be a leading global city, ranking among eighth in the Global Cities Index of 2012 and seventh in the Global Power City Index of 2011. The metropolis is involved in many global affairs, exerting rising influence as the host of the fifth most international conferences worldwide in 2010. It is one of the world's top ten financial and commercial centers, home to major multinational conglomerates such as Samsung, LG and Hyundai-Kia. In 2008, Seoul was named the world's sixth most economically powerful city by Forbes. Seoul was voted the top travel destination by Chinese, Japanese and Thai tourists for a third consecutive year in 2011.

Seoul has a highly technologically advanced infrastructure. It was the world's first city to introduce mobile TV DMB and wireless broadband WiBro, both serviced in all subway lines and buses along with 4G LTE and WiFi. It has the world's fastest 100 Mbit/s broadband network, which at 34.4% has the highest penetration in the world. Seoul Station is the main terminal of the KTX bullet train and the Seoul Subway is the world's second most highly used, featuring the longest circular line and second longest fully underground line in the world. Seoul has a unified public transportation system with Incheon and Gyeonggi, allowing passengers to transfer freely from either subway or bus using the T-money smart card and is connected via AREX to Incheon International Airport, rated the best airport worldwide since 2005 by Airports Council International.

Seoul hosted the 1986 Asian Games, 1988 Summer Olympics, 2002 FIFA World Cup and the 2010 G-20 Seoul summit. The city was named the World Design Capital for 2010 by the International Council of Societies of Industrial Design.