We discuss the role of tetraquarks in the phase transitions of QCD. For three very
light flavors, tetraquarks may generate a second chiral phase transition. In
the plane of temperature and chemical potential ($T$ and $\mu$), tetraquarks must
be included in order to use effective models to determine the position of the critical
endpoint. The tetraquark condensate is the (color invariant) square of the condensate for
color superconductivity. Hence it is natural that in the plane of $T$ and $\mu$, a crossover line for tetraquarks connects smoothly to the transition line for color superconductivity.
|Preferred Track||New Theoretical Developments|