The observation of the unexpected XYZ resonances has challenged the ordinary heavy quarkonium framework, and their microscopic nature remains an unsettled topic. A comprehensive description of this sector will be a major step into the understanding of the QCD spectrum, and of hadron amplitudes in general, and eventually will allow us to improve the hadronic uncertainties which affect precision physics. We discuss the features of amplitude analysis, and the implementation of 3-body unitarity. 

We show how this can help in distinguishing the possible microscopic scenarios. We also show how the large production cross-section of the X(3872) at colliders, together with the comparison with light nuclei production data, disfavors a loosely-bound molecule interpretation, and calls for a new interpretation
for the exotic hadron resonances.