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.