Prior to World War II, Koh Chang was little known. During this period, the few families there made a living growing coconuts and fruit.
During World War II, when Thailand was occupied by Japanese forces, Koh Chang was the scene of the 1941 Battle of Koh Chang between the Royal Thai Navy and a Vichy French naval squadron, in which the French won a decisive victory.
Ko Chang is part of an archipelago of 51 islands, and is approximately 30 km long by 14 km, wide with a total area of 217 km². It is part of the Mu Ko Chang National Park, which covers an area of 650 km², of which 70% is offshore.
It is a mountainous island, with Khao Salak Phet being the highest peak at 743 metres. The island is known for several waterfalls, thriving coral reefs, and rainforests.
The main settlements on the west coast are around Sai Khao, Hat Kai Mook, and Hat Ta Nam, with the village of Bang Bao on the south coast.
Koh Chang is home to populations of the stump-tailed macaque, the small Indian civet, the small Asian mongoose, 61 bird species, and a number of snakes and deer.
The Koh Chang Wart Frog (Limnonectes kohchangae) was originally thought to be an endemic species, but has also been found on the mainland.
The island forms a district (amphoe) in the province of Trat. It was formed on 30 April 1994, when it was split off from Laem Ngop District, at first being classed as a minor district (king amphoe).
Following a decision of the Thai government on 15 May 2007, all of the 81 minor districts were upgraded to full districts. With its publication in the Royal Gazette on 24 August, the upgrade became official.
The district is subdivided into the two subdistricts (tambon) of Ko Chang (Thai: เกาะช้าง), consisting of four villages and with a total population of 3,010, and Ko Chang Tai (Thai: เกาะช้างใต้), five villages with 2,346 inhabitants.
Koh Chang has no airport, with the nearest airport being in Trat on the mainland. Koh Chang Air Taxi offers a seaplane service.
There are two main roads on Koh Chang, running the length of the east and west coasts. Both roads start at Ao Sapparot in the north, near the ferry piers. Shorter roads branch out to Ploytalay Resort and Keereephet, Khlong Nueng, and Klong Phu waterfalls.
Songthaew operate on the two main roads, providing both public transport and taxi services.
Motorbike rental and motorbike-taxis are available.
The nearest long distance road transport is at Trat town, from where the 310 km journey to Bangkok takes five hours by bus.
Ferries run from Laem Ngob in Trat town to Koh Chang, connecting with Ao Sapparot pier, Dan Kao pier, and Laem Ngob pier.
Long-tail boats are available for transport to and from nearby islands.
Koh Chang's income derives largely from tourism, but some traditional livelihoods still exist. Many of Koh Chang's villages rely on fishing, with Ban Salak Phet (Thai: บ้านสลักเพชร) being the largest and oldest community on Koh Chang, in a sheltered location in the south of the island. Other fishing villages include Bang Bao (Thai: หมู่บ้านประมงบางเบ้า), at Bang Bao Beach, which consists of houses on stilts built into the sea, and Ban Khlong Son, which also partly relies on rubber plantations.
Ban Dan Mai and Ban Khlong Non Si also have coconut plantations, and orchards of lychee trees. The variety of lychee grown, Silaman 200 years, is believed to be found only on Koh Chang.
The first foreign backpackers started arriving on Koh Chang in the mid-1970s, using local fishing boats, when the island was still undeveloped.
In 1982, Koh Chang along with the surrounding area became part of the protected Mu Koh Chang National Park, with approximately 85% of the island, together with nearby coral reefs, falling within the park.
It has since become a major tourist destination, both for foreigners and Thais, with a number of tourist resorts being developed.
Despite this, tourism on Koh Chang remains considerably less developed than on Ko Samui or Phuket.
The hilly nature of the island provides it with a number of popular waterfalls, including Klong Plu (น้ำตกคลองพลู). It is the only one on the west side of the island, and has an entrance three kilometres from Ao Khlong Phrao. Waterfalls on the east side of the island include Klong Nonsi, Klong Nueng, Khiri Petch which is about three kilometres from Salak Petch village, the five waterfalls of Kongoi near Bang Bao, and the Thanmayom waterfall near Thanmayom pier.
Ban Salak Phet village has a temple, Wat Salak Phet, built in the reign of King Rama V on his visit to the island. The original temple is now used as a museum commemorating the king's visits to the area. A new temple was completed nearby in 2014.
Bays include Ao Salak Phet, the largest on the island, and Ao Bai Lan (Thai: อ่าวใบลาน).
Koh Chang's beaches include Hat Kai Bae (Thai: หาดไก่แบ้) beach, and Hat Khlong Phrao-Laem Chaiyachet (Thai: หาดคลองพร้าว-แหลมไชยเชษฐ์) beach. By far the busiest is the first beach visitors reach when they arrive on the island, White Sand Beach (Hat Sai Kao). Backpackers will opt to head a couple of kilometres south of Kai Bae Beach to Lonely Beach, which is known for cheap accommodation and almost nightly parties in high season. A quieter alternative is Klong Kloi Beach on the south coast of Koh Chang. This was deserted until 2006 but is now home to a community of beach bars, restaurants, and accommodation.
Koh Chang Yutthanavi Day, which occurs in late January at the Koh Chang Yutthanavi Memorial on Laem Ngop, commemorates the Royal Thai Navy's engagement against the French at the Battle of Ko Chang on 17 January 1941. There is an exhibition by the Royal Thai Navy, and merit-making and tribute rites are performed.