Tom yum is a soup originating from Thailand. It is perhaps one of the most famous dishes in Thai cuisine.
It is widely served in neighboring countries such as Malaysia, Singapore, and Indonesia, and has been popularized around the world.

Tom yum is characterized by its distinct hot and sour flavors, with fragrant herbs generously used. The basic broth is made of stock and fresh ingredients such as lemon grass, kaffir lime leaves, galangal, shallots, lime juice, fish sauce, tamarind, slices of ginger and crushed chili peppers.

In Thailand, tom yum is usually made with prawns (tom yum goong), chicken (tom yum gai), fish (tom yum pla), or mixed seafood (tom yum talay or tom yum po taek) and mushrooms - usually straw or oyster mushrooms. The soup is often topped with generous sprinkling of fresh chopped coriander (cilantro) leaves.

The less popular variety of tom yum is tom yum nam khon, where coconut milk is added to the broth. This is not to be confused with tom kha or tom kha gai - where the galanga flavor dominates the soup. Tom yum nam khon is almost always made with prawns, whereas chicken is often used in tom kha. Its other cousin is less well-known outside Thailand - tom klong. Sometimes Thai chili jam (Nam Prik pao) is added: this gives the soup a bright orange colour and makes the chili flavor more pronounced.

Commercial tom yum paste is made by crushing all the herb ingredients and stir-frying in oil. Seasoning and other preservative ingredients are then added. The paste is bottled or packaged, and sold around the world. Tom yum flavored with the paste may have different characteristics to that made with fresh herb ingredients.