Starting from a small area cell published in 1993, CuInS2 technology has been continuously improved with respect to performance and manufacturability. Major milestones include successful preparation by rapid thermal processing, a monolithically integrated module test structure on a 5 x 5 cm(2) substrate, implementation of an industrial pilot line, incorporation of gallium for higher open circuit voltages and better performance and demonstration of Cd-free devices. Phase formation, reaction pathways and interdiffusion mechanisms have been investigated and modelled as have been electronic and device properties such as current transport. This review summarizes the most significant aspects of development and our current understanding of the technology. (C) 2010 Elsevier B.V. All rights reserved.