Kathmandu, officially the Kathmandu Metropolitan City, is the seat of federal government and the most populous city in Nepal. As of the 2021 Nepal census, there were 845,767 inhabitants living in 105,649 households and approximately 4 million people in its surrounding agglomeration. It is located in the Kathmandu Valley, a large valley surrounded by hills in central Nepal, at an altitude of 4,344 feet (1,324 metres) above sea level.

The city is one of the oldest continuously inhabited places in the world, founded in the 2nd century AD. The valley was historically called the Nepal Mandala (the name for the cosmic elements of water Dha mandala in Newari, and cosmos), and has been the home of the Newar people, a cosmopolitan urban civilization in the Himalayan foothills. The city was the royal capital of the Kingdom of Nepal and hosts palaces, mansions and gardens built by the Nepali aristocracy. It has been home to the headquarters of the South Asian Association for Regional Cooperation SAARC) since 1985. Today, it is the seat of government of the Federal Democratic Republic of Nepal, established in 2008, and is part of Bagmati Province.

Kathmandu is and has been for many years the centre of Nepal's history, art, culture, and economy. It has a multi-ethnic population within a Hindu and Buddhist majority. Religious and cultural festivities form a major part of the lives of people residing in Kathmandu. Tourism is an important part of the economy in the city. In 2013, Kathmandu was ranked third among the top ten upcoming travel destinations in the world by TripAdvisor, and ranked first in Asia. The city is considered the gateway to the Nepal Himalayas and is home to several World Heritage Sites: the Durbar Square, Swayambhu Mahachaitya, Bouddha and Pashupatinath. Kathmandu valley is growing at 4 per cent per year according to the World Bank in 2010, making it one of the fastest-growing metropolitan areas in South Asia, and the first region in Nepal to face the unprecedented challenges of rapid urbanization and modernization at a metropolitan scale. It is the largest metropolitan area located in the Himalayas.