Trends in the production of highly charged ions

This paper will concentrate on the present state of the art of one type of highly charged ion sources used as injectors in cyclotrons and linacs, the electron cyclotron resonance ion source (ECRIS), summarizing general design principles and presenting technical innovations applied in the construction of this type of ion sources. In order to increase the performance of the ECRIS is necessary to increase the confinement time of the ions and the plasma density. The main ingredients to reach these goals are strong magnetic fields and high microwave frequencies. The continuous advance in the last three decades of the superconducting magnet technology was the main driving force in the spectacular development of these ion sources. Several projects under design or construction will be presented.