Baghdad ( BAG-dad or bəg-DAD; Arabic: بَغْدَاد, romanized: Baghdād, [baɣˈdaːd] ) is the capital of Iraq and the second-largest city in the Arab world after Cairo and the second-largest city in West Asia after Tehran. It is located on the Tigris river. In 762 AD, Baghdad was founded as the capital of the Abbasid Caliphate, and became its most notable major development project. Within a short time, the city evolved into a significant cultural, commercial, and intellectual center of the Muslim world. This, in addition to housing several key academic institutions, including the House of Wisdom, as well as a multi-ethnic and multi-religious environment, garnered it a worldwide reputation as the "Center of Learning".

For much of the Abbasid era, during the Islamic Golden Age, Baghdad was the largest city in the world. Its population peaked at more than one million people. The city was largely destroyed at the hands of the Mongol Empire in 1258, resulting in a decline that would linger through many centuries due to frequent plagues and multiple successive empires. With the recognition of Iraq as an independent state (formerly the British Mandate of Mesopotamia) in 1932, Baghdad gradually regained some of its former prominence as a significant center of Arab culture, with a population variously estimated at 6 or over 7 million. Compared to its large population, it has a small area at just 673 square kilometers (260 sq mi).

During the Iran–Iraq War (1980–1988) and the Gulf War (1990–1991), Baghdad faced huge losses. The city has faced severe infrastructural damage due to the Iraq War (2003–2011), which began with the United States-led invasion of Iraq, the subsequent insurgency (2011–2013) and renewed war (2013–2017), resulting in a substantial loss of cultural heritage and historical artifacts. During this period, Baghdad had one of the highest rates of terrorist attacks in the world. However, terrorist attacks have gradually been on the decline since the territorial defeat of the Islamic State militant group in Iraq in 2017, and are very rare now.

As capital of Iraq, Baghdad is home to government offices and diplomatic missions. It is home to numerous landmarks, popular as tourist spots, such mosques, churches, synagogues, malls and hotels. The city serves as an important gateway hub to Iraq, through the Baghdad International Airport. Ethnically, Baghdad is a diverse city, with Arabic-speaking Sunni Muslims as a majority, while Assyrians, Armenians and Jews are a minority, making the city cosmopolitan.