Having at least one parent of Thai nationality helps when applying for citizenship in Thailand. 

As for anyone who does not have a direct Thai link in their heritage, gaining citizenship is complex and relies on laws that are vague.

History has shown that the Thai Kings bestowed Thai citizenship on foreigners who benefitted Thailand.  Therefore, it is not impossible to gain Thai citizenship.  However, it will require knowledge of the Thai language, which means an alphabet and script that is not western. It also involves living in the country for a lengthy period of time. 

Given the changes in the Thai government, it is suggested that anyone interested in obtaining dual citizenship with Thailand contact the Thai Consulate in their area, or their native consulate in Thailand.

An alien with Permanent Residency Status may be eligible to apply for Thai citizenship after five (5) consecutive years of residency.