Abstract: Effects related to electromagnetically induced transparency (EIT), such as controllable linear absorption and dispersion, as well as enhanced nonlinearity, provide many unique properties for ideal optical media. By understanding the fundamental linear and nonlinear optical properties of such coherently-prepared multi-level atomic systems, one can design and make use of the novel properties for various applications in optical communication and quantum information processing. In this short review we will only present the very basic (linear and nonlinear) optical properties of EIT-related atomic media, and briefly mention a few interesting applications.