This article investigates the cooperative guidance problem for multiple missiles to intercept a maneuvering target. We propose an optimal encirclement guidance, which is known to be suitable for improving the observability and limiting the evasive probability of the target. By formulating the optimization problem in a reference frame, the optimal guidance solution can be obtained without any linearization and explicit cooperation can be ensured in regulating the relative line-of-sight angles to achieve encirclement. The main advantage of the proposed approach lies in its nonlinear nature and hence it is more tolerable to disadvantageous initial homing conditions than the linear laws. The working principles and characteristics of the encirclement guidance law are analyzed to support its application. Extensive numerical simulations are performed to validate the proposed approach and demonstrate its advantages.