If travelling to Ko Phangan during or near the time of the Full Moon Party, booking ferry transport to and from the island ahead of time is highly advised as the limited amount of ferries fill up quickly with the massive crowd coming in for the party.
Upon arrival at the pier, pick up a free guide book phangan.info, with a lot of useful information for travelers (ferry timetables, prices of taxi boats, taxi trucks, where to eat, what to do/see, party dates, maps, accommodations, and more) and even some discount vouchers.
Via Ko Samui Airport The closest airport is Ko Samui (USM IATA) which has frequent flights from Bangkok and Phuket, daily flights from U-Tapao and Singapore, and several direct flights each week from Chiang Mai, Hong Kong, Kuala Lumpur and Penang. Transportation to the ferry dock is easy to find at the airport. Ferries depart several times a day with the last one around dusk.
Via Surat Thani Airport The next nearest airport is Surat Thani (URT IATA) on the mainland. Flights from Bangkok there are significantly cheaper (1,000-1,500 baht in advance, or 2,000-2,500 baht if booked same day, instead of 3,000-5,000 baht if flying to Samui), as there are low-cost carriers (Air Asia) flying there, and even Thai Airways charge 30-50% less than to Samui. However, you'll then need combined bus + boat travel to get to Ko Pha Ngan, which will surely take several hours. Air Asia uses Don Mueang airport in Bangkok, while Thai Airways uses Suvarnabhumi airport.
Nok Air sells a combined package ticket including airfare to Surat Thani, Chumphon, or Nakhon Si Thammarat, a bus ride to the pier, and a ticket on the [httpː//www.lomprayah.com Lomprayah high-speed catamaran]. This should be simpler for travellers than arranging the individual segments separately. Nok Air uses Don Mueang Airport in Bangkok.
Air Asia has a special “Island Transfer” offering that includes a flight from Bangkok to Surat Thani or Nakhon Si Thammarat, surface transport to the port, and a ferry to Ko Pha Ngan.
One of the best options for travel to the island is via Chumphon Airport (CJM IATA), 30 km north of Chumphon city in Pathio District (alternative spelling Pathiu). It has direct daily flights connections with Bangkok's two airports, Don Meueng (DMK) and Suvarnabhumi (BKK). There are also onward flights to Ranong Airport (UNN). Flights from Bangkok are around 60 minutes. High-speed Lomprayah catamarans depart from Chumphon to Ko Pha Ngan. Nok Air operates two daily flights between Don Mueang (DMK) and Chumphon Airport (CJM). Nok Air offer a combined flight and ferry ticket on their website. Happy Air [dead link] operates a flight between Bangkok Suvarnabhumi (BKK) to Chumphon 6 days a week. The Chumphon Airport has transit agents for onward connecting travel to the islands of the Chumphon Archipelago in the Gulf of Thailand and Ko Tao, Ko Pha Ngan. The TAT Tourism Authority of Thailand has an information counter at the airport.
Several types of ferries are available, of varying speed and quality. The Lomprayah catamaran is easily the best option for comfort and speed, although generally 100-150 baht more expensive than the other ferries, most travellers and locals, will happily pay the extra for the service.
From Ko Samui: There are at least 3 ferries a day from Ko Samui's "Big Buddha" pier directly to Haad Rin. Ferries also leave from Nathon and Mae Nam piers to Thong Sala several times a day.
Raja Ferry sails from Ko Samui to Thong Sala pier 3 times a day (09:00, 14:00, 18:00) for 150 baht. Tickets can be bought online.
Watch out for scammers at Ko Samui airport who try to sell you a bus/boat combo for an exorbitant price. Make sure to walk towards the exit of the airport where there is an Information counter and taxi stands.
From Ko Tao: there is fast Lomprayah catamaran operating twice a day to Ko Tao for 400 baht at 08:30 and 13:00 or leaving Ko Tao for Ko Pha Ngan at 09:30. The ride between these islands takes 1¼ hours. A cheaper, but slower ferry operates from Ko Pha Ngan to Ko Tao by Songserm express and costs 300 baht, leaving Ko Pha Ngan at 12:30, and takes 2 hours. This ferry comes from Chumphon with flight, bus and train connections from Bangkok.
From Surat Thani: There are ferries throughout the day from Donsak pier, 65 km out of town. Lomprayah are fast ferries and they sell tickets including transport from the city centre for 550 baht.
Raja are slow ferries and combined bus and ferry tickets from the city or Surat Thani train station are available for 375 baht. There are six ferries a day, the timetable is available online. The tickets can be bought online as well.
Night ferry leaving at 23:00 from Surat Thani city (walking distance from bus stations Talat Kaset 1 and 2), arriving in Thong Sala-Ko Pha Ngan at 06:00. It costs 400 baht for a space on a mattress on the boat. The night ferry leaves from Thong Sala-Ko Pha Ngan for Surat Thani at 22:00 (400 baht) arriving around 05:00-06:00.
The best way in by bus is by government bus (บขส) to the Na Dan ferry piers: these are the most direct, quickest, reliable, safest, and hassle-free services. Tickets for these services can be bought at Sai Tai Taling Chan (southern) government bus terminal in Bangkok.
Buses also arrive in Surat Thani, capital of Surat Thani Province. From here you can buy a ticket for a bus + boat ride for the slow ferry (320 baht for the 3-hour ferry and bus ticket to Don Sak) or the fast ferry (400 baht for the 2-hour ferry + transportation to Don Sak pier). Both ferries stop at Ko Samui first, and will drop you off at the pier of Thong Sala. Please note that both options will require you to change buses. This should be a quick and easy change over.
If there are no available options listed above (usually only if you've arrived to the bus terminal quite late in the evening before a weekend or holiday), you can also try a bus to Chumphon and board a ferry there, see "By train" below. You can buy a combo ticket on the bus station, it will cost same as if purchased separately (and the bus arrives 2–3 hours before ferry departure, so you shouldn't be late).
Buses originating from Khao San Rd (or other buses operated by travel agencies) are famous for thefts from passenger luggage. Under no circumstances should passengers on Khao San Rd buses leave valuables in bags that will go in the luggage storage areas, even if the bags can be locked. Consider it inevitable that every bag will be opened while the bus is in motion. Bus + boat joint ticket costs at the cheapest Israeli travel agencies at the west end of Khao San Rd (better said Chakrapong Rd) cost only 500-550 baht depending on whether it's before/after Full Moon Party and your bargaining skills, so if you are aware of risks using these buses and careful you can really save money instead of taking pricier government bus which does not leave from KSR but requires you to go to a bus terminal.
A very good option, a little pricier, is using the morning bus (06:00) and ferry combination from Lomprayah. A reputable company with an office near Khao San Rd and the option to book online through their website. The air-con bus is very new and the connection to the ferry gives the opportunity for a toilet break and to eat something. Leave early in the morning and arrive mid/late afternoon on the island. One way is 1,300 baht. They also have a night bus.
An overnight train from Bangkok is an interesting option. Trains arrive in Surat Thani or Chumphon, and from there you can transfer by bus and then boat. Chumphon is the option if you're planning to stop at Ko Tao, but if you're heading straight to Ko Pha Ngan, consider Surat Thani. Both stations are on the southbound Hat Yai line, but arrival times in Chumphon (when using night trains) are annoyingly early in the morning. For example, the (recommended) express train number #85 arrives around 04:00 after which you'll have to wait about 3 hours for the ferry. On the other hand, if you continue down to Surat Thani you can sleep an extra 3–4 hours plus you will arrive in daylight. Considering the waiting time in Chumphon and the longer ferry trip you will eventually get to Ko Pha Ngan at about the same time.
Combined train-bus-boat tickets can be bought direct from the official Advance Booking Counter at Hualamphong station in Bangkok, although if your train is late, and your boat is already gone then you will have to pay extra for the next boat. Thus the joint ticket may not be the best choice.
If e-booking is not available or not suitable to you for some reason, train tickets may be reserved up to 60 days in advance and paid for by email. In reality, the Thai authorities are lax in returning emails and/or will give the runaround, or flat-out refuse to reserve seats for non-Thais during peak travel periods (Dec-Jan and the Songkran holiday in Apr). If your heart is set on going by train, start early, be persistent, and have a backup plan to go by bus or plane.