Stars form through the gravitational collapse of cold, dense molecular clouds, while planets emerge within the circumstellar disks of protostellar systems. In this talk, I present studies carried out with my students over the past several years to better understand the origins of stars and planets. Using radio observations at (sub)millimeter wavelengths, we investigate both molecular clouds, which define the initial conditions of star formation, and protostellar disks, where planets are born. Particular emphasis will be placed on the role of magnetic fields in molecular clouds as a primary regulator of star formation, as well as on the substructures and grain growth detected in protostellar disks as tracers of early planet formation.