Surat Thani (Thai: สุราษฎร์ธานี, pronounced [sù.râːt tʰāː.nīː]), often shortened to Surat, is the largest of the southern provinces (changwat) of Thailand. It lies on the western shore of the Gulf of Thailand. Surat Thani means 'city of good people', a title given to the city by King Vajiravudh (Rama VI); Surat Thani is therefore the sole province in Southern Thailand for which the native name is in the Central Thai language.

Surat Thani Province, located in Thailand, is bordered by the provinces of Chumphon to the north, Nakhon Si Thammarat to the east, Krabi to the south, Phang Nga to the southwest, and Ranong to the northwest.

The geographic landscape of Surat Thani is diverse. The central region of the province is dominated by the coastal plain of the Tapi River, characterized by a mix of grassland, rubber trees, palm oil trees, and coconut plantations. To the west lie the limestone mountains of the Phuket range, largely enveloped in forest, home to the renowned Khao Sok National Park. The eastern part of the province sees the commencement of the Nakhon Si Thammarat (or Bantat) mountain range, a portion of which is preserved within Tai Rom Yen National Park. The total forest area in Surat Thani is approximately 3,764 km² (1,453 sq mi), accounting for 28.8 percent of the province's area.

Several islands in the Gulf of Thailand are part of Surat Thani, including popular tourist destinations such as Ko Samui, Ko Pha Ngan and Ko Tao, as well as the Ko Ang Thong Marine National Park.

The province is also defined by its main waterways, the Tapi River and the Phum Duang River, which converge near the town of Tha Kham before emptying into Bandon Bay. The delta formed by these rivers, known locally as Nai Bang (ในบาง), is situated directly north of Surat Thani city. This delta features a network of channels interspersed with small islands, predominantly covered by mangroves and orchards.

There are a total of eight national parks, six of which are in region 4 (Surat Thani) and Hat Khanom–Mu Ko Thale Tai and Namtok Si Khit are in region 5 (Nakhon Si Thammarat) of Thailand's protected areas.

There are two wildlife sanctuaries, along with five other wildlife sanctuaries, make up region 4 (Surat Thani) of Thailand's protected areas.

The region of Surat Thani has a long history of human habitation, dating back to prehistoric times. It was initially inhabited by indigenous Semang and Malayan tribes. In the 3rd century, the area came under the influence of the Srivijaya kingdom, a powerful entity that controlled much of the Malay Peninsula until the 13th century. The city of Chaiya, located in modern-day Surat Thani, is home to several archaeological ruins from the Srivijaya period, indicating its historical significance. There is a belief among some Thai historians that Chaiya may have served as a regional, or possibly even the primary capital of the Srivijaya kingdom, although this assertion remains a subject of scholarly debate. Another notable settlement from this era was Wiang Sa, which also played a significant role during the time of Srivijaya's dominance.