Transport from Suvarnabhumi Airport (BKK) Thailand to Siem Reap, Cambodia is pretty simple. Follow the signs to the bus stop on the arrivals side of the airport. Catch the next bus to Morochit station and buy your ticket to Aranyaprathet, Thailand there. Prices are approximately $16 per person. This was an “express bus” (16 passenger van) that departs when full. From my experience, they depart every 15-20 minutes during business hours. There is one stop along the way prior to arrival at the border. My trip took about 2.5 hours because the driver was going pretty fast. Some drivers may take longer.
The van will stop in front of a business that offers an expedited visa service. I am not so sure it is necessary but I chose this option because their service was not much more than the visa cost. In my case, the company helped with the paperwork and hand carried my passport through the process. Their total time was about 20 minutes but they advised me of an hour wait in line for people who were not using a service.
Once you get your passport back, the company walked me the 100 yards to the boarder and shortly thereafter I was in Cambodia.
On the Cambodian side, there are swarms of people trying to provide taxi service to Siem Reap. Ignore them and take the shuttle to the bus transport station for $1 or $2. From there, the buses depart at regular intervals and cost under $9 for the 4 hour ride.
Many people advise that Cambodia does not use other currency. Not true! Avoid the poor exchange rates by making exchanges in Siem Reap at banks or other reputable companies. US Dollars will work just fine until you get there. As pictured, the currency is in small denominations and looks like a lot for under $100.
I hope this helps with your boarder crossing. If you need any additional information, just ask your question in the comment box below.