The ever-impressive food journal Gastronomica published a history of the origins of Pad Thai. While considered THE quintessential Thai dish by many Americans, Pad Thai’s origins are significantly murkier, and is much less common in Thailand itself than in Thai restaurants in other countries.Within Thailand we had our only Pad Thai experience on Khao San road, an area notorious for its amounts of European and North American backpackers. The Pad Thai vendors there were definitely catering to an audience! The full name of the dish, Kway teow pad Thai even indicates Pad Thai may even have Chinese origins. Check out the Gastronomica article for a full history of Pad Thai.
Our picture of some stateside Pad Thai
Eating The World 
The Thais in Thailand would eat Pad Thai from street vendor not from the restaurants because there are only a few restaurants that can make this dish decent enough. Next time you go to Bangkok, try Sukhumvit soi 38 (Sky train Thonglor station). There is a vendor there that serve one of the best Pad Thai in Bangkok. Also there is another one on Silom Rd. near Soi Convent.
Originally a Vietnamese dish, the Vietnamese name which i can’t remember means street food i think.