A constructive control strategy for the stabilization of the inverted pendulum system is presented, under the assumption that the pendulum is initialized above the upper half plane. To do so, a suitable procedure to find a candidate Lyapunov function for the whole system is developed. Then, the control is proposed directly from the Lyapunov function, in such a way that its time derivative is semi-definite negative with respect to a convenient manifold. Finally, the asymptotically stability of the closed-loop system is concluded by LaSalle theorem.