Phacopidae is a family of phacopid trilobites that ranges from the Lower Ordovician to the Upper Devonian, with representatives in all paleocontinents.

However, several phacopids have very few lenses, such as the species of the genera Cryphops, Denckmannites, Dienstina, Eucryphops, Nephranops, and Plagiolaria, or lack eyes altogether, like Afrops, Dianops, Ductina, and Trimerocephalus.

The natural fracture lines (sutures) of the head run along the top edges of the compound eye.

The thorax has 11 (rarely 10) segments, the side lobes (or pleurae) are furrowed, and the articulating facets distinct.

In many Phacopidae, where the facial sutures are apparently continuous and well developed, they were evidently nonfunctional in ecdysis, since no separate free cheeks can be found.