The Thai greeting referred to as the wai (Thai: ไหว้, pronounced [wâːj]) consists of a slight bow, with the palms pressed together in a prayer-like fashion. It has its origin in the Indic Añjali Mudrā, like the Indian namasté and the Cambodian sampeah. The higher the hands are held in relation to the face and the lower the bow, the more respect or reverence the giver of the wai is showing. The wai is traditionally observed upon entering formally a house. After the visit is over, the visitor asks for permission to leave and repeats the salutation made upon entering. The wai is also common as a way to express gratitude or to apologise.

The word often spoken with the wai as a greeting or farewell is Sawasdee (สวัสดี, RTGS: Sawatdi, pronounced [sàwàtdiː]). This word was coined in the mid-1930s by Phraya Upakit Silapasan of Chulalongkorn University. This word, derived from the Sanskrit svasti (meaning "well-being"), had previously been used in Thai only as a formulaic opening to inscriptions. The strongly nationalist government of Plaek Pibulsonggram in the early 1940s promoted the use of the word sawasdee amongst the government bureaucracy as well as the wider populace as part of a wider set of cultural edicts to modernise Thailand.