The upper part of the body makes up nearly two thirds of the body weight yet usually it is looked at as only being passively carried by the legs. Although the role of the upper limbs in walking is indeed secondary to that of the lower limbs, their movements are not purely passive. In the first half of the paper, we introduce a novel method to control a biped with a torso to walk stably. In this control method, there is only one low gain PD controller between the torso and the stance leg, with the swing leg remaining totally free. Simulation results show that, by adopting this controller, the biped robot can walk over a range of step period and a wide range of step length. In the second part of the paper, we use an optimisation-based approach to predict the walking motion of a simple biped with a torso.