Since ten years ago experiments have been observing a host of exotic states decaying into heavy quarkonia. The interpretation of most of them still remains uncertain and, in some cases, controversial. Notwithstanding, a considerable progress has been made on the quality of the experimental information available and a number of ideas and models have been put forward to explain the observations. We will review the most promising theoretical interpretations of exotic states, in particular we will discuss the nature of the charmonium-like resonances in the region 3850−4050 MeV, and propose a new mechanism to explain prompt X(3872) production cross section at hadron colliders. Finally, the phenomenology of doubly charmed states is commented.