Las Vegas, colloquially referred to as Vegas, is the most populous city in the U.S. state of Nevada and the seat of Clark County. It is the 24th-most populous city in the United States, with 641,903 residents at the 2020 census. The Las Vegas metropolitan area has an estimated 2.4 million residents and is the 29th-largest metropolitan area in the country. Las Vegas is an internationally renowned major resort city, known primarily for its gambling, shopping, fine dining, entertainment, and nightlife. Most of these venues are located in downtown Las Vegas or on the Las Vegas Strip, which is outside city limits in the unincorporated towns of Paradise and Winchester. The Las Vegas Valley serves as the leading financial, commercial, and cultural center in Nevada.

Las Vegas was settled in 1905 and officially incorporated in 1911. At the close of the 20th century, it was the most populated North American city founded within that century. Population growth has accelerated since the 1960s and into the 21st century, and between 1990 and 2000 the population increased by 85.2%.

The city bills itself as the Entertainment Capital of the World, and is famous for its luxurious and large casino-hotels. As of 2023, Las Vegas attracts over 40.8 million visitors annually, making it one of the most visited cities in the United States and consistently ranking among the world's top tourist destinations. It is the third most popular U.S. destination for business conventions and a global leader in the hospitality industry. The city's tolerance for numerous forms of adult entertainment has earned it the nickname "Sin City," and has made it a popular setting for films, literature, television programs, commercials and music videos.

In 1829, Mexican trader and explorer Antonio Armijo led a group consisting of 60 men and 100 mules along the Old Spanish Trail from modern day New Mexico to California. Along the way, the group stopped in what would become Las Vegas and noted its natural water sources, now referred to as the Las Vegas Springs, which supported extensive vegetation such as grasses and mesquite trees. The springs were a significant natural feature in the valley, with streams that supported a meadow ecosystem. This region served as the winter residence for the Southern Paiute people, who utilized the area's resources before moving to higher elevations during the summer months. The Spanish "las vegas" or "the meadows" (more precisely, lower land near a river) in English, was applied to describe the fertile lowlands near the springs. Over time, the name began to refer to the populated settlement.

Nomadic Paleo-Indians traveled to the Las Vegas area 10,000 years ago, leaving behind petroglyphs. Ancient Puebloan and Paiute tribes followed at least 2,000 years ago.

A young Mexican scout named Rafael Rivera is credited as the first non-Native American to encounter the valley, in 1829. Trader Antonio Armijo led a 60-man party along the Spanish Trail to Los Angeles, California, in 1829. In 1844, John C. Frémont arrived, and his writings helped lure pioneers to the area. Downtown Las Vegas's Fremont Street is named after him.

Eleven years later, members of the Church of Jesus Christ of Latter-day Saints chose Las Vegas as the site to build a fort halfway between Salt Lake City and Los Angeles, where they would travel to gather supplies. The fort was abandoned several years afterward. The remainder of this Old Mormon Fort can still be seen at the intersection of Las Vegas Boulevard and Washington Avenue.^{[citation needed]}

Las Vegas was founded as a city in 1905, when 110 acres (45 ha) of land adjacent to the Union Pacific Railroad tracks were auctioned in what would become the downtown area. In 1911, Las Vegas was incorporated as a city.