For French citizens, a visa is not required for stays of 1 to 30 days.
If your trip exceeds 30 days, you must apply for a tourist visa at a Thai embassy or consulate.
Required documents include:
The original passport + one photocopy (valid for at least 6 months after entering Thailand)
2 recent ID photos
A photocopy of your plane ticket (round trip recommended)
A completed and signed visa application form
A bank statement showing a minimum balance of €1,000
A hotel reservation
€30 to cover the visa fee
The tourist visa allows you to stay 60 days. Once in Thailand, you can extend it for an additional 30 days at any immigration office. The extension costs 1,900 baht (approximately €50).