The muscle peroneus longus (also known as fibularis longus) is a superficial muscle in the human leg, and acts to evert and plantar flex the ankle.

It is attached proximally to the head of the fibula and its 'belly' runs down most of this bone.

Peroneus longus becomes a tendon that goes posterially around the lateral malleolus of the ankle, then continues under the foot to attach to the 1st metatarsal.

It is a muscle of the lateral compartment of the leg and is innervated by the superficial peroneal nerve.