Acid mine drainage (AMD) from both active and abandoned mine sites is a major environmental issue for the mining industry in environmentally concerned regions of the world. This chapter describes the sources and chemical and biological reactions resulting in AMD. It covers the measures to prevent AMD formation and the methods to manage their environmental impacts. There are five major sources of AMD, namely, drainage from underground workings, run-off and discharges from open pits, waste rock dumps, tailings, and ore stockpiles. The processes that occur in the accretion and migration of AMD are controlled by both physical and chemical factors. Local environmental conditions also play an important role in the accretion and migration of AMD. Various physical, chemical, and biological control measures have been used to prevent, minimize, and treat AMD. Basically, there are two types of prevention and control, the first relates to the generation of AMD, while the second relates to its in situ mobilization and subsequent migration.