  Ion sources are a critical component of all particle accelerators. They
create the initial beam that is accelerated by the rest of the machine. This
paper will introduce the many methods of creating a beam for high-power hadron
accelerators. A brief introduction to some of the relevant concepts of plasma
physics and beam formation is given. The different types of ion source used in
accelerators today are examined. Positive ion sources for producing H+ ions and
multiply charged heavy ions are covered. The physical principles involved with
negative ion production are outlined and different types of negative ion
sources are described. Cutting edge ion source technology and the techniques
used to develop sources for the next generation of accelerators are discussed.
