Highly charged ions are the most chemically reactive species known to mankind. This reactivity is due to the extremely large potential energy they posses. This textbook deals with the wide range of interactions which occur when such ions interact with other forms of matter, especially solid surfaces and gasses. Particular emphasis is placed on situations where the kinetic energy associated with the interactions is small so that the effects of the high potential energy are most apparent. Experimental and theoretical techniques of investigation are covered in addition to the findings they produce. The treatment aims to be instructive to the beginner while leading on to a level where the newest findings are reviewed.