Development of the Different RFQ Accelerating Structures and Operation Experience

Fourteen years after the invention of the "spatially continuous strong focusing" principle in the USSR and five years after the start of the RFQ research program in the USA numerous (~ 15) laboratories all over the world are concerned with this new accelerator concept and many projects are under way. In this paper a brief review of these activities and the considered applications is given and the different approaches in beam dynamics, electrode configuration and resonators are outlined.