Located in the Gulf of Thailand at about 350km to the south-east of Bangkok downtown, Koh Chang is in fact the third largest island of the country with its 30 km long and 14 km wide, forming an area of 211 km² (81.46 sq mi) just behind Phuket (543 km² - 209.7 sq mi)  and Koh Samui (238 km² - 91.89 sq mi) and within an archipelago of 54 islands.
But if you add the areas of all the small islands around Koh Chang, it makes this one the second largest island of Thailand, just between Phuket and Koh Samui.
Second or Third doesn't really matter as long as it stays a Paradise island!

Koh Chang means the "elephant island" because of the shape of the mountains which look like the head of an elephant. You can see this shape when you are at White Sand beach or from the sea on the south-west side of the island.
Other people say the name comes from the shape of the island which looks like an elephant head. The bay of Salak Phet in the south east of the island looks like the trunk of the elephant.
Different people and different beliefs!

 
Because 70% of the island is covered by a tropical forest, also called rain forest of even jungle by the tour operators, this island is different from the other tourists places of Thailand. 
Most of the buildings are located on the west coast and the center of the island is covered by a deep vegetation that the bravest can explore with a guide.

Koh Chang and the islands around belong to the National Park and are of course protected. Some of those small islands can be discovered by kayak or by boat.

The western part of the island is the most visited and the most populated. 
The white sandy beaches are located on the west side while the east side is more rocky. Most of the tourists stay on the west near the main beaches but you can find small quiet pieces of paradise if you go away from the main road or even on the eastern part of the island.

There are all types of accommodation in Koh Chang, from the luxurious resorts to the small bungalows, for every budgets. Some will offer air-conditioning, free Wi-Fi, bathroom with hot water while others will only get a fan and cold water. 
When you are booking a room, be sure to know in advance what you will get and what you will not get. It will avoid bad surprises.

Don't worry before preparing your trip to Koh Chang, there are a lot of shops and drugstores where you can find all what you need, from the sun lotions to the anti-antibiotics. Of course all kind of food and drinks can also be bought in the small markets. You will not be lost.

Like the shops, there are also lots of pubs and restaurants along the island for all kind of people. Some of them are owned by foreigners who have brought a part of their culture. Do not be amazed to find Belgian, Irish or German beers as well as Italian ice-creams or French wine and cheese. In Koh Chang you can find everything!