What We Can Learn from Heavy Exotic States

In the last 20 years many states were discovered in the heavy quark sector that do not fit into the classification provided by the until then very successful quark model.  After a thorough introduction I will focus on multi-quark states and explain the various proposals existing for the structure of the unconventional states, how to distinguish between them experimentally and what they will eventually teach us about the inner workings of the theory of the strong interaction, QCD, and the formation of matter.