The QCD axion is probably the most robust solution to the strong CP problem and a natural dark matter candidate. While its properties, such as the mass and the couplings, are mostly determined by non-perturbative QCD effects I will present recent computations demonstrating that they can be reliably extracted with percent accuracy, which is important for the theory interpretation of experimental results. I will also discuss some recent
lattice QCD results highlighting a departure from the usual instanton
estimates and potentially changing the prediction for the axion relic
abundance substantially.