UPDATED! TEST & GO rules to ease from 1 March 2022

The following new rules will be in effect from 1 March, 2022 (travellers can enter into Thailand on 7 March, 2022).
Points of entry:

By air (direct international flight or transit domestically via dedicated flights.)
By land (at the border checkpoints in Nong Khai, Udon Thani, and Songkhla.)
By water (yachts.)
Eligible travellers / countries:

For arrivals by air and water: Thai citizens and foreign travellers from all countries/territories.
For arrivals by land: Thai citizens and foreign travellers from neighbouring countries connecting with the reopened border checkpoints (Nong Khai, Udon Thani, and Songkhla).
Entry registration system:

For arrivals by air and land: Thailand Pass system.
For arrivals by water: Certificate of Entry system.
Quarantine requirement:

For arrivals by air and land: No quarantine, but on Day 1 must wait for the COVID-19 test result within an approved SHA Extra Plus (SHA++) or alternative quarantine facility.
For arrivals by water: No quarantine, but on Day 1 must wait for the COVID-19 test result on board the travelling vessel (yacht).
Accommodation requirement:

A proof of prepayment for 1 night of accommodation at government-approved hotel/s; such as, SHA Extra Plus (SHA++) on Day 1.
Health insurance:

An insurance policy with coverage no less than US$20,000. Thais and foreign expatriates under Thailand’s national healthcare coverage are exempt from this requirement.
COVID-19 testing requirements:

For arrivals by air and land: First test on Day 1 by an RT-PCR method (wait for the result within the hotel), and the second test on Day 5 by a self-ATK method (must report/record the result via the application).
For arrivals by water: First test on Day 1 by an RT-PCR method (wait for the result on board the vessel), and the second on Day 5 by a self-ATK method (must report/record the result via the application).
Existing requirements/rules remain unchanged:

A Medical Certificate with an RT-PCR lab result indicating that COVID-19 is not detected issued no more than 72 hours before travelling.
A Certificate of COVID-19 Vaccination/Recovery.
Current Rules
(An update that reflects the new rules will be available from 1 March, 2022, onwards.)
Fully vaccinated travellers from any country around the world can apply for a TEST & GO Thailand Pass under the following requirements.
Eligible travellers
• Thai citizens.
• Foreign travellers, including but not limited to diplomats, guests of the government, Thai work permit holders, students and their family, and patients seeking medical treatment.

Eligible countries
• All countries/territories.
Pre-Arrival Requirements
All travellers must have the following documents for entering Thailand:

A Thailand Pass, which can be applied via https://tp.consular.go.th/.
A Medical Certificate with an RT-PCR lab result indicating that COVID-19 is not detected issued no more than 72 hours before travelling.
Travellers under 6 years of age, travelling with parents with a negative RT-PCR test result within 72 hours before travelling, are not required to have a pre-arrival negative RT-PCR test result and can have a saliva test when entering the Kingdom.
For arrivals by water, everyone on board the vessels must have a medical certificate with an RT-PCR lab result indicating that COVID-19 is not detected within the officially specified time frame. Anyone on aboard with a history of COVID-19 infection within a period between 14-90 days must have a medical certificate of recovery.
An insurance policy with coverage no less than US$50,000. TAT recommends that travellers make sure to check the small print of any COVID-19 insurance policy before purchasing. Ultimately, the policy should cover the cost of treatment and other medical expenses associated with being infected with COVID-19, including in-patient hospitalisation, hospital isolation, hotel isolation, or related quarantine. The insurance policy should also cover the whole duration that travellers are planning to stay in Thailand, plus at least 10 extra days as a precautionary measure in the event that the traveller’s second swab test result returns as positive.
Thais and foreign expatriates under Thailand’s national healthcare coverage are exempt from this requirement.
A proof of prepayment for 2 separate nights of accommodation at government-approved hotel/s, such as, SHA Extra Plus (SHA++), AQ, OQ, or AHQ on Day 1 and Day 5, and the expenses for 2 RT-PCR tests on Day 1 and Day 5.
The prepayment for Day 1 must include an accommodation, a test and a prearranged transfer from the airport to the hotel.
Travellers can book 2 different hotels for the accommodation on Day 1 and Day 5. However, on both Day 1 and Day 5, they must stay within the room for the RT-PCR test result.
The second RT-PCR test will not be required if the traveller’s length of stay is less than 5 nights, or his/her scheduled international departure date out of Thailand is on Day 5 or before. For example if the traveller plans to stay in Thailand for 3 days, then he/she does not have to undergo the second RT-PCR test, but he/she must leave for another country immediately. However, whether the traveller will be required to take another RT-PCR test depend on the airline and the final international destination.
A Certificate of COVID-19 Vaccination/Recovery
Everyone 18 years of age and older must be fully vaccinated for COVID-19 with an approved vaccine at least 14 days before travelling to Thailand.
Travellers 12-17 years of age travelling to Thailand unaccompanied must get vaccinated with at least 1 dose of an approved vaccine. Those travelling with parents are exempt from this requirement.
Travellers 6-11 years of age, travelling with parents, are exempt from this requirement.
For arrivals by water, everyone on board must be fully vaccinated. This is except for travellers under 18 years of age, travelling with parents or guardians.
Travellers with a history of COVID-19 infection who have recovered by medical treatment, and travellers who have received at least 1 dose of an approved vaccine after post-infection must have a certificate of COVID-19 recovery.
All travellers must undergo ‘exit screening’ at the point of departure, i.e., at the airline check-in counter and present the required documents to the person-in-charge to carry out the checks.

On-Arrival Requirements / During the Stay
All travellers must undergo ‘entry screening’, including body temperature check at the point of entry.
Present the required documents to the Immigration/Health Control officer to carry out the checks, then proceed through the Immigration procedures.
Proceed to the prearranged accommodation or medical facility to undergo the first RT-PCR test. The trip must be by a prearranged vehicle on a sealed route. Then, all travellers must wait for the test result within the hotel only. Travellers under 6 years of age, travelling with parents, can have a saliva test.
If testing negative for COVID-19, travellers are free to go anywhere in Thailand. However, they must stay at their prepaid accommodation on Day 5 and undergo their second COVID-19 test using the RT-PCR technique (they must stay within the room for the RT-PCR test result.) The second test can also be taken when the travellers experience respiratory symptoms.
Travellers whose test result returns as positive will be referred for appropriate medical treatment in accordance with Thailand’s Communicable Diseases Act B.E. 2558 (2015). The expenses must be covered by the required insurance for foreign travellers, or national healthcare coverage for Thais and eligible foreign expatriates. TAT recommends that travellers make sure to check the small print of any COVID-19 insurance policy before purchasing. Ultimately, the policy should cover the cost of treatment and other medical expenses associated with being infected with COVID-19, including in-patient hospitalisation, hospital isolation, hotel isolation, or related quarantine. The insurance policy should also cover the whole duration that travellers are planning to stay in Thailand, plus at least 10 extra days as a precautionary measure in the event that the traveller’s second swab test result returns as positive.
Pending on their conditions, they may be medically advised to receive treatment in either hospital hotel isolation or community isolation.
During receiving the medical treatment – at least 10 days, they must remain in their accommodation only. They should not leave their accommodation unless utmost necessary, and must notify the Communicable Disease Control officer in-charge.
After having recovered from COVID-19, they will receive a medical certificate of recovery.
While in Thailand, travellers are advised to strictly follow standard, good personal hygiene practices; such as, wear a mask in public, maintain hand hygiene (washing with soap and water or using hand sanitizer), and keep physical distance of at least 1 metre from others.
Travellers who are experiencing COVID-like symptoms should get tested. If testing positive they must get an appropriate medical treatment. Those with COVID-19 testing appointment must get tested.
All travellers must download and install the MorChana application, and set it on at all times for the COVID-19 precautionary measures and to record the result on Day 5-6 in the application.
Meanwhile, travellers who have applied/obtained their Thailand Pass QR code before 22 December, 2021, with scheduled arrival dates in Thailand from 24 December, 2021, onwards, are still required to undergo their second COVID-19 test using the RT-PCR technique at government-designated facilities on Day 5-6 of their stay in Thailand, or when they experience respiratory symptoms (no additional cost).
Guidelines for Domestic/International Departure
For domestic departure, travellers must show proof that they have received a negative result for their RT-PCR test.

For international departure, it is the responsibility of travellers or their organisations to make sure that the travellers meet the requirements of their specific international destination regardless of the point of departure.