Beyond the stellar light of the galaxy which is visible in broad-band optical emission, there exist multi-phase gases, dust, cosmic ray, and magnetic field, which more or less fill in the dark matter halo or even to larger scale. These matters are often called the circum-galactic medium (CGM), which play a critical role in the co-evolution of galaxies and their environments. I will briefly overview the basic observational methods and key results of existing multi-wavelength observations of the multi-phase CGM. I will show that although the CGM is ubiquitous around nearby galaxies, the physics related to the CGM, as well as the role of CGM is galaxy formation and evolution, are still poorly understood. Some new observations with future space- and/or ground-based facilities will help us to better understand the CGM.
