Planetary magnetism is important because it informs us about the internal structures of planets and moons and throws light on their origins and evolutions. Magnetic fields protect a planet from the particles and radiation flowing from the Sun. A planetary magnetic field is likely necessary for life to exist. There is ample motivation for the study of planetary magnetic fields. In this talk I will summarize what we know about the magnetic fields of the planets and moons in our solar system and what these fields reveal about their host planets. I will discuss planets that had magnetic fields in the past as revealed by the remanent magnetization of their crusts. I will describe the observations of induced magnetic fields in the Galilean satellites of Jupiter that have led to the discovery of subsurface liquid water and magma oceans. I will note that the south polar plumes on Enceladus were first discovered by the magnetometer on the Cassini spacecraft. I will point out why the unusual magnetic field of Saturn prevents us from determining the planet's period of rotation. Clearly, magnetic fields are involved in a broad range of planetary phenomena and I end my talk with the admonition that planetary travelers should never leave home without a magnetometer.