There are two fundamental visa options for a visitor to Thailand from most countries :
THAILAND VISA WAIVER
These are the countries allowed to enter Thailand under the VISA EXEMPTION RULE
Argentina, Australia, Austria, Bahrain, Belgium, Brazil, Brunei ,Canada, Chile, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hong Kong, Hungary, Iceland, Indonesia, Ireland, Israel, Italy, Japan, Korea, Kuwait, Laos, Liechtenstein, Luxembourg, Macau, Malaysia, Monaco, Mongolia, Netherlands, New Zealand, Norway, Oman, Peru, Philippines, Poland, Portugal, Qatar, Russia, Singapore, Slovak Republic, Slovenia, South Africa, Spain, Sweden, Switzerland, Turkey, United Arab Emirates, United Kingdom, United States, Vietnam.
To do so, a foreigner must possess a valid passport or travel document that is recognized by the Royal Thai Government and comply with the conditions set forth in the Immigration Act B.E.2522 (1979) and its related provisions.