The Acmon Blue (Plebejus acmon) is a North American butterfly. It ranges mainly in California but can be seen north to Oregon and south through Baja California. The tops of the wings are blue with dark edges in males and brown in females. Its underside is white with black spots for both sexes with a red-orange band on the hindwing. Adults feed on nectar while caterpillars can feed on buckwheats, lupines, trefoils, and milkvetches.

Like many other Lycaenid butterflies, it has a mutualistic relationship with ants, who protect Acmon Blue larvae in exchange for honeydew that the larvae secrete.