The humble current-voltage (I-V) measurement has proven to be an extremely powerful probe of the physics of condensed matter systems from bulk semiconductors and superconductors to quantum dots and nanotubes. However, doing these deceptively simple measurements "right" so as to unambiguously extract particular bits of physics is hard. This is especially true of charge and spin density wave (CDW and SDW) conductors and related collective transport systems, in part because of the tremendous richness of their physics. The central role of the CDW I-V characteristic in experiment has made it the focus of extensive theoretical study, and the ideas developed have spread to many areas of condensed matter physics. In this short review 1 discuss some highlights of the study of the CDW I-V characteristic. After nearly 30 years, the fundamental experimental features are finally becoming clear, and they are not accounted for by existing theories. © EDP Sciences.