Probably two most popular around the world Thai dishes are: the Tom Yum (or Tom Yam) soup and the Pad Thai.
The Tom Yum soup is a delightful combination of spicy hot and sour, with flavor provided by the lemon grass, lime leaves, galangal, fish sauce, and the hot by chili. Its basis forms the broth with spices, additions are typically mushrooms and shrimps/ prawns. Tom Yum Goong is the name of the soup with prawns. Tom Yum soup is very popular in Thailand and in Laos. It is also served in Malaysia and Singapore