I hold a Chinese passport so I needed a visa on arrival which allows me to stay 15 days. I got mine at the Chiang Mai airport within 10min. Mind you this is slow season so expect time variance in peak seasons.
For the visa you need:
- a valid passport
- one 4x6cm passport photo
- a simple form to be filled with your Thai accommodation address
- more than 2000baht Thai money in cash (about 65USD) *This amount changes from time to time. Mine was actually 2200baht*
- the official site requires a return ticket, however I was not asked to present one, neither was my friend who holds a Canadian passport. However I’d still prepare one in case they do ask to avoid being refused to enter
- the official site also mentions that open tickets, travelling overland out of Thailand by train, bus, etc to other countries is not accepted as exiting proof
Overall it was a very smooth process, friendly staff, clear signs, straight forward steps.