Title: Magnetic Fields in the Milky Way and the Magellanic Clouds
Description: This thesis is an observational investigation into the origin of large-scale coherent magnetic fields in the Milky Way and the Magellanic Clouds. I use Faraday rotation measure of both polarized extragalactic sources and that derived from diffuse polarized synchrotron emission as probes of interstellar magnetism. Rotation measure uniquely provides the magnetic field direction in the diffuse interstellar medium, which cannot be achieved using other observing techniques.