The present paper aims at generating three-dimensional cyclic gait of a biped with a locomotion system having anthropomorphic characteristics. Kinematic and dynamic models of both single and double support phases are extensively developed with a special attention devoted to the double support phase. A variety of gait constraints defining a feasible walk is taken into account. Joint trajectories are approximated by cubic spline functions connected at uniformly distributed knots. Joint coordinates at knots, walking phase durations, and independent parameters at phase transitions are the design parameters of a parametric optimization problem. Therefore, only the pattern organization and the gait speed are explicitly specified. The effectiveness of the proposed method is verified and discussed through some simulation results.