Phnom Penh (another Romanization: Phnum Pénh. Loosely translated: "Mount Penh" or "Penh's Hill", named after a wealthy matriarch called Lady Penh, is the capital and largest city of Cambodia. Located on the banks of the Mekong River, Phnom Penh has been the national capital since the French colonized Cambodia, and has grown to become the nation's center of economic activities. Phnom Penh has grown to become the industrial, commercial, cultural, tourist and historical center of Cambodia.

Once known as the "Pearl of Asia", it was considered one of the loveliest of French-built cities in Indochina in the 1920s. Phnom Penh, along with Siem Reap and Sihanoukville, are significant global and domestic tourist destinations for Cambodia. Founded in 1434, the city is noted for its beautiful and historical architecture and attractions. There are a number of surviving French colonial buildings, such as the Royal Palace, Phsar Thmei, and other French style buildings along the grand boulevards.

Situated on the banks of the Tonlé Sap, Mekong and Bassac rivers, Phnom Penh is home to more than 2 million of Cambodia's population of over 14 million. It is the wealthiest and most populous city in Cambodia and is home to the country's political hub.

The oldest structure is the Wat Phnom from the founding days of the city, constructed in 1373. The main tourist attractions are the Royal Palace with the Silver Pagoda, which dates to the mid-19th century; the National Museum, constructed during the French colonial era in the late 19th century in the classical Khmer style hosts a vast collection of Khmer antiquities; the Independence Monument (Khmer: Vimean Akareach), although modern from the 1950s, is also constructed in the ancient Khmer style.

The French, who were the colonial masters from the 19th century to the 1940s, also left their mark, with various colonial villas, French churches, boulevards, and the Art deco market Phsar Thom Thmei. A notable landmark of the colonial era is the Hotel Le Royal.

Starting with independence from the French in the 1950s and lasting until the era of the Khmer Rouge in the 1970s, Phnom Penh underwent tremendous growth as the capital city of a newly independent country. King Sihanouk was eager to present a new style of architecture and thus invigorate the process of nation building. A new golden era of architecture took off, with various projects and young Khmer architects, often educated in France, given opportunities to design and construct. This new movement was called "New Khmer Architecture" and was often characterised by a fusion of Bauhaus, European post-modern architecture, and traditional elements from Angkor. The most prominent architect was Vann Molyvann, who was nominated chief national architect by the king himself in 1956. Molyvann created landmark buildings such as the Preah Suramarit National Theatre and the Council of Ministers building, other architects helped construct the newly founded Royal Khmer University, the Institute of Foreign Languages and the National Sports Centre. With the growth of the upper and entrepreneurial middle class, new suburbs were built in the 1950s and 60's.

Although these buildings survived the Khmer Rouge era and the civil war, today they are under threat due to economic development and financial speculation. Villas and gardens from that era are being destroyed and redeveloped to make place for bigger structures. The landmark National Theatre by Molyvann was ripped down in 2008. A movement is rising in Cambodia to preserve this modernist heritage. Old villas are sometimes being converted into boutique hotels, such as the Knai Bang Chatt.

Monuments and memorials to the genocide during the Khmer Rouge era in the 1970s are the Tuol Sleng Genocide Museum (a former high school used as a concentration camp) and on the outskirt of the city the Choeung Ek Genocide Center. The Cambodia-Vietnam Friendship Monument was commissioned by the Vietnamese communists as symbol of Khmer-Vietnamese "friendship" during the late 1970s following the liberation of Cambodia from the Khmer Rouge.