A tour of the XYZ states at BESIII

Quarkonia, mesons made from a heavy quark and anti-quark, are considered to be the strong interaction analogues to the hydrogen atom. As such, the spectrum of the c\bar c charmonium hadrons can be calculated using familiar methods
from quantum mechanics. Experimentally, below the threshold for the decay into pairs of charm-flavoured hadrons the observed states fit the calculations very well. Above that threshold, however, experiments have found a large number
of new, exotic hadrons that do not match our expectations for regular quarkonium hadrons - the XYZ states.
In e+e- annihilation experiments like BESIII, vector mesons with the same spin and parity as the photon are produced copiously, and indeed exotic vector-states like the Y(4230) have been reported. Exotic states with different
spin-parity like the X(3872) and Zc(3900) are produced in radiative and hadronic decays of the vector mesons. Their interpretation is still a matter of hot debate. In this talk, I will discuss recent results in an ongoing effort to
shed light on the regular and exotic charmonium above the open-charm threshold.