Tom yum or tom yam is a family of hot and sour Thai soups. It is a soup that normally includes shrimp. The strong, hot, and sour flavors make it very popular in Thai cuisine. The name "tom yam" is composed of two Thai words. Tom refers to the boiling process, while yam means 'mixed'. Historian Giles Milton contends that the origins of Tom Yum can be traced back to India, where there is a variation of hot and sour shrimp soup known as "sour prawn soup."

Citrus hystrix, called the kaffir lime, Thai lime or makrut lime, is a citrus fruit native to tropical Southeast Asia.