Thai curries are always made with a curry paste. Common ingredients used in many Thai curry pastes are:
- Shrimp paste
- Chillies; depending on the curry these can be dried or fresh, red or green
- Onions or shallots
- Coriander (cilantro) root
Depending on the type of curry, additional ingredients for the paste can include spices such as turmeric, pepper, coriander seeds, cardamom pods, and cumin, or other ingredients such as boiled fermented fish, and fingerroot. The ingredients for the curry paste are ground together, traditionally with a mortar and pestle and non-traditionally with an electric food processor. With many curries, the paste is first stir-fried in cooking oil before other ingredients are added in to the dish. Due to the oil's reaching higher temperatures than boiling water, this technique releases certain flavours from the spices and other ingredients in the paste which would not have been possible by only boiling it.
Both khrueang kaeng (lit. "kaeng ingredients") and nam phrik kaeng (lit. "kaeng chilli paste") are used to describe "curry paste" in Thailand. The latter is sometimes even shortened to only phrik kaeng (lit. "kaeng chilli").
Thai curry pastes can be made at home from the bare ingredients, bought freshly made at markets in Thailand, or they can be had packaged at shops and supermarkets.