The QCD axion is well-studied as a solution to the Strong CP problem and a dark matter candidate. At the same time, one often hears that axions are ubiquitous in top-down string theory models of particle physics. I will discuss how both bottom-up and top-down considerations favor axion models where the axion is a mode of a higher-dimensional gauge field. I will provide a viewpoint on why the existence of axions could follow from general principles of quantum gravity, and what we might expect the QCD axion's properties to be.