The Kathmandu Valley (Nepali: काठमाडौं उपत्यका); also known as the Nepal Valley or Nepa Valley (Nepali: नेपाः उपत्यका, Nepal Bhasa: 𑐣𑐾𑐥𑐵𑑅 𑐐𑐵𑑅, नेपाः गाः), is a bowl-shaped valley located in the Himalayan mountains in Nepal. It lies at the crossroads of ancient civilizations of the Indian subcontinent and the broader Asian continent, and has at least 130 important monuments, including several pilgrimage sites for Hindus and Buddhists. There are seven World Heritage Sites within the valley.

The Kathmandu Valley is the most developed and the largest urban agglomeration in Nepal with about 5 million population. The urban agglomeration of Kathmandu Valley includes the cities of Kathmandu, Lalitpur, Budhanilkantha, Tarakeshwar, Gokarneshwar, Suryabinayak, Tokha, Kirtipur, Madhyapur Thimi, Bhaktapur,Changunarayanetc. The majority of offices and headquarters are located in the valley, making it the economic hub of Nepal. It is popular with tourists for its unique architecture, and rich culture that includes the highest number of jatras (festivals) in Nepal. Kathmandu valley itself was referred to as "Nepal Proper" by British historians. As per the World Bank, the Kathmandu Valley was one of the fastest growing metropolitan areas in South Asia with 2.5 million population by 2010 with an annual growth rate of 4%.

In 2015, Kathmandu Valley was hit by the April 2015 Nepal earthquake. The earthquake caused thousands of deaths and the destruction of much infrastructure across the Kathmandu Valley, which includes the towns of Lalitpur, Kirtipur, Madhyapur Thimi,Changunarayan,Bhaktapur. Kathmandu is also the largest city in the Himalayan hill region.