As they are first optimized for their ion losses, ECRISs are always under a fundamental compromise: having high losses and strong confinement at the same time. To help ECR ion source developers in the design or improvement of existing machines, general comments are presented in a review article being soon published. In this 160 pages contribution, fundamental aspects of ECRISs are presented, with a discussion of electron temperature and confinement and ion confinement. Then, as microwaves play a key role in these machines, a chapter presents major guidelines for microwave launching and coupling to ECR plasma. Moreover, once ECR plasma is created, understanding this plasma is important in ion sourcery; and a section is dedicated to plasma diagnostics with an emphasis on the determination of electron and ion density and temperature by vacuum ultraviolet (VUV) spectroscopy. Another chapter deals with the role of magnetic confinement and presents updated scaling laws. Next chapter presents different types of ECRISs designed according to the main parameters previously described. Finally, some industrial applications of ECRISs and ECR plasmas in general are presented like ion implantation and photon lithography. Some hints taken from this review article are presented in the following article.
