The paper surveys the 20 or so decades of frequency of the electromagnetic spectrum, and discusses both the energy and information which can be extracted from it. The Sun provides abundant radiant energy, which is being used to an increasing extent to provide terrestrial power.The history and use of radio waves, the visible spectrum, and X, γ and cosmic rays are examined. In recent years optical astronomy has received a boost from competition by radio astronomy. All available parts of the spectrum are now being used by both Earth and satellitebased instruments. There is rapidly-growing knowledge about the Universe and its probable origin in the Big Bang.