The aims of Advances in Physics: X are to demonstrate: 1. the connectivity of Physics, by which we mean the intellectual relationships between one branch of Physics and another; and 2. the pervasiveness of Physics, that is, the influence of Physics across (hence the “X”) the boundaries into other disciplines, including chemistry, materials science, engineering, biology, and medicine. Thus the journal promotes the centrality of Physics and physical measurement to modern science and technology, defending the discipline and revealing both its richness and its impact. The aims of APX are achieved through the Open Access, electronic publication of concise review articles, commissioned from leading experts and made available freely throughout the world.