The book describes the story of the activities of electron, the first subharmonic particle before and after its identification by Sir J.J.Thomson, at the Cavendish Laboratory, Cambridge, UK in 1897. The activities of the electron prior to its discovery like static charge, current flow, radio transmission and reception, generation and distribution of electricity, heating and lighting effects are dicussed, The identification of the electron is presented as a detective story. The development of the vacuum pump, the discharge lamp, the Crookes’ Tube have been introduced as tools of investigation. The atomic structure, and dual nature, particle and wave of the electron are briefly discussed. The discovery of ‘hole’, and the joint venture of the electron and hole in developing present Solid-state Technology are treated as ‘Further Investigation’, Both Vacuum tubes and their uses, and solid state devices like transistors, photoelectric devices, op-amps, microprocessors, LEDs, solar cells are discussed.