There has always been a trade-off between the stability and the energy consumed by a bipedal robot. Therefore, current research trends towards building bipeds which can balance the existing trade-off between the energy consumed by the robot and its stability. This book presents an energy and stability functions, incorporating the stability parameters of the Zero Moment Point (ZMP) classed bipeds. The stability parameters are the positions of Center of Mass (CoM) and ZMP respectively. The Energy function is derived using the concept of Orbital Energy.