Xi'an is the capital of the Chinese province of Shaanxi. A sub-provincial city on the Guanzhong plain, the city is the third-most populous city in Western China after Chongqing and Chengdu, as well as the most populous city in Northwestern China. Its total population was 12.95 million in the 2020 census, including an urban population of 9.28 million.

Xi'an is one of the oldest cities in China. Known as Chang'an throughout much of its history, Xi'an is one of China's Four Great Ancient Capitals, having held the position under several of the most important dynasties in Chinese history, including the Western Zhou, Qin, Western Han, Sui, Northern Zhou and Tang. Xi'an is now the second-most popular tourist destination in China. The city was one of the terminal points on the Silk Road during the ancient and medieval eras, as well as the home of the 3rd-century BC Terracotta Army commissioned by Emperor Qin Shi Huang—both of which are listed as World Heritage Sites by UNESCO.

Since the 1980s, as part of the economic growth of inland China especially for the central and northwest regions, Xi'an has developed into a cultural, industrial, political and educational, and research and development hub. Xi'an currently holds sub-provincial status, administering 11 districts and 2 counties. In 2020, Xi'an was ranked as a Beta- (global second tier) city by the Globalization and World Cities Research Network, and, according to the country's own ranking, ranked 17th; it is also one of the world's top 100 financial centers according to the Global Financial Centres Index. Xi'an is ranked by the Nature Index as one of the top 20 cities globally by scientific research output, and is home to multiple prestigious educational institutions, such as Xi'an Jiaotong University, Northwestern Polytechnical University, Xidian University and Northwest University.

Xi'an is the atonal pinyin romanization of its Chinese name 西安, Western Peace. (The apostrophe – known in Chinese as a 隔音符號, géyīn fúhào – should be included to distinguish its pronunciation from the single syllable xian.) The name was adopted in 1369 under the early Ming dynasty. Jesuit missionaries recorded its name as Si-ngan or Si-ngan-fou from its status as the seat of a prefecture (府, fǔ). This form still appears in the Latin name of the Catholic diocese of Xi'an, archidioecesis Singanensis. The name was later romanized as Hsi-an by Wade & Giles and as Sianfu or Sian by the imperial post office, both of which were common until the promulgation of pinyin.

The area of present-day Xi'an has been the site of several important former Chinese cities. The capital of the Western Zhou were the twin cities of Feng and Hao, known collectively as Fenghao, located on opposite banks of the Feng River at its confluence with the southern bank of the Wei in the western suburbs of present-day Xi'an. The Qin capital Xianyang was erected north of the Wei during the Warring States period and was succeeded by the Western Han capital of Chang'an (長安), meaning "Perpetual Peace", which was located south of the Wei and covered the central area of present-day Xi'an. During the Eastern Han, Chang'an was also known as the "Western Capital" (西京), named for its namesake position relative to the main capital at Luoyang. Under the Sui, its name became Daxing (大興, "Greatly Prosperous") in AD 581. Under the Tang, the name reverted to Chang'an in 618. Under the Mongolian Yuan dynasty (13th & 14th centuries), it held a succession of names: Fengyuan (奉元), Anxi (安西, "Peaceful West") and Jingzhao (京兆). The Ming name "Xi'an" was changed back to Xijing ("Western Capital", as above) between 1930 and 1943.

The Lantian Man was discovered in 1963 in Lantian County, 50 km (31 mi) southeast of Xi'an, and dates back to at least 500,000 years before the present time. A 6,500-year-old Neolithic village, Banpo, was discovered in 1953 on the eastern outskirts of the city proper, which contains the remains of several well organized Neolithic settlements carbon dated to 5,600–6,700 years ago. The site is now home to the Xi'an Banpo Museum, built in 1957 to preserve the archaeological collection.

Xi'an became a cultural and political center of China in the 11th century BC with the founding of the Zhou dynasty. The capital of Zhou was established in the twin settlements of Fengjing (灃京) and Haojing (鎬京), together known as Fenghao, located southwest of contemporary Xi'an. The settlement was also known as Zōngzhōu (宗周) to indicate its role as the capital of the vassal states. In 738 BC, King Ping of Zhou moved the capital to Luoyang due to political unrest.

Following the Warring States period, China was unified under the Qin dynasty (221–206 BC) for the first time, with the capital located at Xianyang, just northwest of modern Xi'an. The first emperor of China, Qin Shi Huang ordered the construction of the Terracotta Army and his mausoleum just to the east of Xi'an almost immediately after his ascension to the throne.