Siam (Thai: สยาม, RTGS: Sayam, pronounced [sā.jǎːm]) is a shopping district in the heart of Bangkok, the capital of Thailand. It is situated alongside a stretch of Rama I Road in the city's Pathum Wan District, from Pathum Wan Intersection to Chaloem Phao Junction, beyond which it meets the adjacent Ratchaprasong neighbourhood. The area is home to multiple large shopping malls, and, together with Ratchaprasong, forms what has been termed the city's central shopping district, functioning as the modern-day city centre.
The area is named for Siam Square, a low-rise retail area owned and developed by Chulalongkorn University, as well as several enclosed malls opposite it which all bear Siam as part of their names: Siam Discovery, Siam Center and Siam Paragon, the last of which replaced the Siam Inter-Continental Hotel in 2002. The properties occupy land leased from the Sa Pathum Palace, which is privately owned by Prince Mahidol Adulyadej's branch of the Royal Family. Also within the neighbourhood are MBK Center and the Bangkok Art & Culture Centre on opposite corners of Pathum Wan Intersection.
The area's commercial development initially took place during the 1960s and 1970s alongside Ratchaprasong, and together they gradually supplanted the Wang Burapha area as the city's centre of urban retail and youth culture. The BTS Skytrain, which opened in 1999 with its central interchange Siam Station serving the area, helped cement the neighbourhood's prominence.