We present a robust method for measuring the effective plane of the Kuiper belt. The derived plane has an inclination with respect to the ecliptic of 1.86d and an ascending node of 81.6d, with a 1 σ error in pole position of the plane of 0.37d. The plane of the Kuiper belt is inconsistent with the invariable plane, the plane of Jupiter, and the plane of Neptune at the greater than 3 σ level. Using linear secular perturbation theory, we show that the plane of the Kuiper belt is expected to oscillate about the position of the invariable plane with a period of 1.9 million years and an amplitude of 1.2d. The present predicted position of the plane of the Kuiper belt has an inclination with respect to the ecliptic of 1.74d and an ascending node of 86.7d, within 0.20d of our measured position.