Using light, electrons, or X-rays, microscopes today form a vital tool not only in biology but in many other disciplines, including materials science and nanotechnology. In this Very Short Introduction Terence Allen describes the scientific principles behind the main forms of microscopy, and the exciting new developments in the field. Beginning with a brief history of microscopy, Allen surveys the diverse and powerful forms of miscroscopes available today, illustrating how microscopy impinges on almost every aspect of our daily lives.