The cephalon is the foremost portion of the segmented body of a trilobite. Generally this region of the body can be thought of as the "head" of the animal, including the eyes on the dorsal surface of the body, and the hyperstome (part of simle mouth) on the venter (underside), directly below the anterior edge of the glabella. It is composed to chitin, and usually fossilizes well.

Most cephalons are shaped like the front most portion of horse-shoe crabs, though there is extremely wide variation in trilobite morphology.