Bang Rak (Thai: บางรัก, pronounced [bāːŋ rák]) is one of the fifty districts (khet) of Bangkok, Thailand. It lies on the eastern bank of the Chao Phraya River, beyond Khlong Phadung Krung Kasem, which marked the old city boundary. Originating from riverside settlements dating from before the city's foundation, Bang Rak grew inland as new roads and canals were constructed through the area during the second half of the nineteenth century and the early twentieth, attracting communities of expatriates and developing into a major commercial district.

Bangkok's rapid economic growth in the late twentieth century saw the areas along Si Lom and Sathon roads transformed into one of the city's main business districts, teeming with skyscrapers. The district, officially recognised at least since 1908, covers an area of 5.54 square kilometres (2.14 sq mi), and has a registered population of 48,227 (as of 2019).

Up until the mid-nineteenth century, water formed the primary mode of transport in the lower Chao Phraya plains, and most people lived along the banks of rivers and canals. Settlements had formed along the Chao Phraya River since the Ayutthaya Kingdom (14th century – 1767), and some Buddhist temples in and around Bang Rak date to the period. Bangkok became the capital city with the foundation of the Thonburi Kingdom in 1767, and was re-established as the Rattanakosin Kingdom in 1782; riverside areas beyond the fortified city of Rattanakosin Island developed into fringe neighbourhoods settled by various ethnic communities. Downstream of the city and just beyond the Chinatown area, the waterfront stretch that is now Bang Rak Subdistrict was home to Thais, Chinese, Vietnamese, Malays, Lao, Tavoyans, and descendants of Portuguese, among others. A Catholic church (now in the adjacent Talat Noi neighbourhood), dedicated to the Lady of the Rosary, was established by the Portuguese community in 1787. French priests then moved into the area for missionary work, followed by Protestants, mostly from the United States.

As international trade increased in the nineteenth century, the neighbourhood developed into one of many port areas along the river.

By the time of King Mongkut's reign (Rama IV, 1851–1868), the city had outgrown its original defensive walls, and the King ordered the digging of Khlong Phadung Krung Kasem to serve as a new outer moat surrounding the city proper. The canal separated Bang Rak, on the far side from the city, from the Chinatown area, and as the country began modernizing and opened to the West under Mongkut's reign, European visitors began establishing themselves here. The Bowring Treaty was signed with the British in 1855, liberalizing trade and granting diplomatic concessions, and other Western countries followed suit. Consulates, trading companies and expatriate communities were established in the waterfront area, which became the city's European quarter.

The Westerners also indirectly set off the city's transformation. They petitioned Mongkut to build roads for their use, first to the Phra Khanong area (to where they planned to relocate but later abandoned the idea), then to serve the waterfront community in Bang Rak. The King obliged, and had Thanon Trong (also known as Hua Lamphong Road and later to become Rama IV Road) constructed in 1857 and Charoen Krung Road in 1862. Si Lom Road soon followed, linking the two. The introduction of land-based transport transformed the city, and Charoen Krung became its main thoroughfare, bringing commerce and spurring development.

In the 1890s and 1900s, during the reign of King Chulalongkorn (Rama V, 1868–1910), enterprising businessmen engaged in land development by buying up land and building roads through the area. The resulting Sathon, Surawong, and Si Phraya roads ran roughly parallel to Si Lom, and, together with a few connecting roads between them, have since formed the district's main road network.

The development attracted businesses, which established numerous shops along the roads, as well as newly wealthy residents, who made their homes in villas. Emerging ethnic communities were formed by migrants arriving from Western colonies, who found advantage in the treaties' extraterritorial provisions. Among them were Javanese Muslims, and Hindus, Muslims, and Jains from India, who established places of worship in their neighbourhoods, joining the Christian churches as the missionaries continued to expand their work through the founding of schools and hospitals. The roads were soon augmented by rail transport, as the Paknam Railway (the country's first line) opened along Thanon Trong in 1893, and electrified trams began running on Charoen Krung Road the following year. Another tram line, along Si Lom Road, opened in 1925.