Formation processes of negative ions are first described to explain how the negative ion plasma is obtained. Then, natural plasmas, typically the D-layer in the upper atmosphere; other plasmas such as sprites followed by man-made plasmas containing negative ions, typically DC plasmas such as the positive column, hollow cathode discharge, Q-machine, magnetic multipole, and double plasmas; capacitively and inductively coupled radio-frequency discharge plasmas; microwave plasmas of open and electron cyclotron resonance (ECR) types; and helicon plasmas are described. As for other types of negative ion plasmas, double plasma, arc, corona, electron-beam-injected type, pulsed type, afterglow, downstream, double sheath, magnetron, and Penning type are also reviewed. Theoretical approaches, modeling, and simulation for the negative ion plasma are dealt with. Then, diagnostic methods for negative ions using electrostatic probes, laser photodetachment, mass spectrometry, optical emission spectroscopy, and plasma waves are presented. Finally, various applications of negative ion plasma such as surface modification, ion implantation, and negative ion sources for material science and for nuclear fusion and accelerators are presented.