The QCD axion provides a solution to both the strong CP and dark matter problems in the Standard Model. However, the axion solution requires that the gravitational violation of the Peccei-Quinn global symmetry be suppressed to an extremely high order. This so-called axion quality problem can be addressed in 5D models with a holographic (AdS/CFT) interpretation that predict flavor-dependent axion-fermion couplings. Moreover, 5D models also allow for the intriguing possibility that the axion mass could be enhanced while still solving the strong CP problem. These features have implications for the ongoing experimental axion searches and lead to new possibilities in early universe cosmology.