Resonant inverse photoemission spectroscopy (RIPES) is a new spectroscopic probe of the electronic states in solids. It exploits the resonant enhancement of the inverse photoemission cross section occurring at appropriate core absorption edges, and is therefore the counterpart of resonant photoemission for the unoccupied states. We present the results of a RIPES investigation of cerium-based Kondo systems, which illustrate the main aspects of the technique, and briefly review some recent developments involving these and other systems. (C) 1999 Elsevier Science B.V. All rights reserved.