This book describes the development of sources of negative ions and their application in science and industry.  It describes the physical foundations and implementation of the key methods of negative ion production and control, such as charge exchange, thermionic emission, plasma volume, secondary emission (sputtering) and surface-plasma sources, as well as the history of their development. Following on from this essential foundational material, the book goes on to explore transport of negative ion beams, and beam-plasma instabilities. Now in its second edition, the book has been substantially expanded and updated to address the many developments since it was first published, most importantly the development and investigation of cesiated surfaces with work function ~1.2-1.3 eV in conditions close to discharges in surface plasma sources. The book also includes a new chapter on development of conversion targets for high-energy neutral beam injectors, covering gas targets, plasma targets and photon targets for efficient conversion of high energy negative ion beams to neutral beams. With exposition accessible at the graduate level, and a comprehensive bibliography, this book will appeal to all students and researchers whose work concerns ion sources and their applications to accelerators, beam physics, storage rings, cyclotrons, and plasma traps.