In Star Trek, what crystals regulate the matter–antimatter reaction in a warp core?

In Star Trek, dilithium crystals regulate the matter–antimatter reaction in a warp core.

Dilithium is a fictional crystalline substance central to faster-than-light starship travel. In a warp core, matter and antimatter are brought together to produce enormous energy, while dilithium controls the reaction so that the energy can be channelled into the warp engines.

The crystals are not usually described as the fuel itself. Matter and antimatter provide the reaction’s consumable components; dilithium acts as the crucial regulating medium. This distinction is a common source of confusion when fictional propulsion systems are compared with chemical rocket fuel.

Dilithium became one of Star Trek’s most recognizable technical terms after appearing in The Original Series. Later series expanded its history, including stories about dilithium shortages and the catastrophic “Burn” in Star Trek: Discovery. The exact fictional physics changed across productions, but its role as a warp-core regulator remained consistent.