The calf muscle group is made up of three muscles superficial in the posterior compartment of the lower leg, with gastrocnemius and soleus being the main ones.
There are other muscles deep in the posterior compartment of the lower leg: popliteus, flexor hallucis longus, flexor digitorum longus, and the tibialis posterior.
The calf muscles act to plantar flex the ankle joint. In addition, the Gastrocnemius also acts to flex the knee when not weight bearing, and stabilizes the ankle and knee when standing. The plantaris muscle flexes and stabilizes the knee joint.