In recent years, the spectroscopy of hadrons containing heavy quarks has brought forward a plethora of new and unexpected resonance-like signals. Many of these so-called X,Y,Z states are candidates for states beyond the quark-antiquark or three-quark configurations of mesons and baryons, respectively, which have been sought after since the introduction of the quark model. Similar studies in the light-quark sector are more challenging due to the wide and overlapping nature of known resonances. Recent high-quality data samples, collected e.g. by the COMPASS experiment at CERN or at e+e− machines, open the possibility to search for exotics also at masses below 2.5 GeV/c2. In particular, access to hadrons with explicit gluonic degrees of freedom is expected to be easier in this mass region. Recently, lattice QCD started to make predictions on the multiplet structure of such exotic hadrons, which may be used as a guideline in the experimental searches.
Excited states are produced in t- or s-channel reactions or in the decays of heavy hadrons into multi-particle final states subjected to partial-wave analyses. In addition to studying the properties of established mesons with unprecedented accuracy, the large existing data samples allow us to detect possibly exotic states. The talk will give an overview on ongoing experimental studies of light exotic states involving novel analysis techniques and discuss possible interpretations.