Located in the Gulf of Thailand at about 350km to the south-east of Bangkok downtown, Koh Chang is 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.
Lots of people refer Koh Chang as a Paradise and family island.

Koh Chang means the "elephant island". There are different sayings about its name, one says it's 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 southwest side of the island.

View from White Sand Beach
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 southeast of the island looks like the trunk of the elephant.
Different people and different beliefs!

Koh Chang 
Because 70% of the island is covered by a tropical forest, also called rain forest or 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 centre of the island is covered by deep vegetation that the bravest can explore with a guide. Don't underestimate the jungle, every year lots of people think they can manage by themselves and get easily lost. remember that the jungle is also the home of king cobras, tarantulas, pythons, vipers and other reptiles you wouldn't like to meet. A viper or cobra's bite would be lethal.

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, the most developed and the most populated. 
The white sandy beaches are located on the west side while the east side is rockier. 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 on Koh Chang, from the luxurious resorts to the small and cheap huts, for every budget. 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 that you need, from sun lotions to anti-antibiotics. Of course, all kind of food and drinks can also be bought in small markets. You will not be lost.
Koh Chang is a safe island and it's considered a family island, perfect if you travel with children.

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!