In this Tutorial, surface and double charge exchange negative ion sources for producing negative ion beams of different ion species will be described. The need for negative ions as the beam particles of tandem Van de Graaf accelerators and that for charge exchange injection of hydrogen negative ions into high-energy proton accelerators requires the development of these ion sources, which are then enlarged to generate ampere level broad beams to heat up, after neutralization, the fusion experiment plasmas confined in magnetic field. The physical mechanisms leading to the formation of various negative ion species, such as hydrogen, helium, alkali metals, and halogens will be presented, and the ion source designs are analyzed based on the knowledge of fundamental processes related to negative ion formation and destruction. The use of negative ion sources in accelerators, nuclear fusion research, technology, and medicine will also be presented.