Ko Samui Airport (USM) is a private airport originally built by Bangkok Airways , which is still the main operator and was for a long time the only airline with services to Ko Samui from Thailand until Thai Airways started in April 2008 to operate some flights between Bangkok and Ko Samui. They have near-hourly departures to/from Bangkok and tickets are expensive by Thai standards, with advance bookings costing 2000-3500 baht, while a walk-in booking may be twice as much. There are also daily flights to/from Phuket for 2200 baht, U-Tapao, and Singapore; four direct flights a week from Chiang Mai (but no direct flights in the opposite direction); and twice weekly flights to/from Hong Kong.
In addition to Bangkok Air, Ko Samui is served two flights a day from Bangkok with Thai Airways as well as by Berjaya Air  from Kuala Lumpur and Firefly  from Penang and Subang airport (Kuala Lumpur) in Malaysia.
Visa-on-Arrival and Visa-Free entry is available at Samui Airport for some nationalities - see Thailand for more information.
Ground transportation from the airport is readily available. A seat in a minibus for the 20-minute ride to Chaweng costing 100 baht/person; a faster taxi will cost 150-300 baht. Be sure to negotiate the rate to your destination before you get into the taxi since many drivers refuse to use their meters.
A cheaper but less convenient option is to fly to Surat Thani and connect by road and then ferry.
From Surat Thani train station and Surat Thani Airport (URT), there are combined bus/ferry services to Ko Samui cost 200-300 baht - some entail a 60 minute bus ride followed by a 90 minute ferry crossing, others a 30 minute bus ride but the ferry takes extra time. Tickets are sold by numerous agents that meet each train and airport. Should cost less than 300 baht (return combo ticket to either Surat Thani city, airport or train station bought on the Na Thon pier on Samui normally costs 220 baht) There are 2 Ferry companies (departures every 30 mins).
Numerous ferry services are direct from mainland Surat Thani include an express boat (3 departures daily, taking around 3 hours and costing 150 baht) and slow night boats (taking 6-7 hours). Call operator Songserm Travel (252 9654 in Bangkok) for the latest schedules, which vary according to the season.
Raja Ferry Port  operates services between Donsak pier (on the mainland about an hour from Surat Thani) and Lipa Noi pier on the western side of Samui.
There are also regular speedboats and ferries to Ko Pha Ngan and Ko Tao.
Lomprayah  offers a combined bus/high speed catamaran ferry service from Bangkok to Ko Samui which takes about 11 hours (5.5 of them by boat) and costs around 1250 baht (1000 baht in the opposite direction). The bus pauses in Hua Hin and then stops at Chumphon, where it connects with the ferry, which calls at Ko Nang Yuan, Ko Tao and Ko Pha Ngan on its way to Ko Samui.
Songthaew transfer from the pier at Lipa Noi on Samui to either Chaweng or Lamai will cost 100 baht per person. Taxis will be more expensive, with initial asking prices of up to 500 baht.
As on many islands in Thailand, small motorbikes are available for rental. Compared to other nearby islands, Samui's road systems is very developed and there are plenty of taxis cruising about, although it's a challenge to get them to use their meters.
The usual panoply of watersports are available, including plenty of dive shops, but most diving is done either in the nearby Angthong Marine National Park or Ko Tao as the visibility around Samui's sandy beaches tends to be poor. You can book diving day trips at dive shops, most of which are based in Chaweng. The dive boats tend to leave from the pier at Bophut and Bang Ruk.
Diving Without a doubt the south of Thailand is home to some of the finest and most beautiful beaches and islands in the world, surrounded by crystal clear water and stunning coral. And that is the main reason why the number of divers coming to Thailand has escalated over the past decade or so. Even though the best time year of the year to dive in the Ko Samui is between June and August, it is still perfectly possible to dive virtually all year round. As diving in Thailand is considered one of the safest destinations for diving and snorkeling in the world, it is perfect for first-timers wanting to try these pastimes out.
The sea visibility in some places around Ko Samui is almost very good (distances of up to 10-30 meters). One can enjoy splendid sights of underwater mountains, coral gardens, undersea rock formations, hard and soft coral, whale sharks.
Samran Pinnacles:' Since the currents in this area are often quite strong, this site is recommended therefore, for experienced divers. Due to the currents being like this, the site is a haven for bringing in larger pelagics such as barracuda, jacks. There are three submerged pinnacles near Sail Rock.
Ko Kra & Koh Losin:' These two small islands located to the south-east of Samui, which because of its remotest, don’t get too many divers. Blacktip sharks, manta rays and hard to find loggerhead turtles can be seen.