Circumstellar disks occur around a wide variety of objects ranging from Young Stellar Objects (T Tauri stars), to rapidly rotating main-sequence stars (Be stars), to Luminous Blue Variables and Proto-Planetary Nebulae. In this talk, I will discuss some of the formation mechanisms for these disks, how we observationally detect them, and how we can determine information about their structue using techniques like spectropolarimetry, infrared and optical imaging, and spectrophotometry.