Chapter 5 AdS-QCD 5.1 Premise In 2005 two very interesting papers [2,113] were published that for the first time dispensed with trying to deform supergravity solutions to mimic QCD. Instead the authors aim was to “start from QCD and attempt to construct its five-dimensional holographic dual”. Since QCD has an infinite number of operators, they had to be careful about which operators they were going to try and include. [2] focused on holographically modelling the dynamics of chiral symmetry breaking in QCD. To this end, we would expect only a small number of operators to be influential. These would be So in keeping with the unique operator-field matching, this would require three fields on the five-dimensional holographic side. Their details are given in table 5.1. 72 • the left-handed and right-handed currents corresponding to the SU ( N$_{f}$ )$_{L}$ × SU ( N$_{f}$ )$_{R}$ chiral flavour symmetry • the chiral order parameter