Science: Since the work of James Clerk Maxwell and Heinrich Hertz, we have known that light is an electromagnetic wave. An intricate mechanism generates magnetic fields around the electric fields, and vice versa. In the optical-wavelength range, experimental studies have been limited to probing only the electric-field components.In Science, Matteo Burresi and colleagues report direct measurements of the magnetic-field components of light obtained with a nanostructured metallic probe at the tip of a sharp glass fiber. Related LinkProbing the magnetic field of light at optical frequencies