Circumstellar disks play an important role in the evolutionary life cycle of stars; they guide the earliest stages of star formation, serve as the birthplace of planetary systems, and shape stellar outflows in the latest stages of stellar evolution. Inspite of their importance, we still do not understand the basic mechanisms which guide the formation and evolution of disks. In this talk, I will discuss a variety of observational efforts to explore the structure and evolution of pre-main-sequence protoplanetary disk systems and near-main-sequence decretion disk systems.