Abstract: This report presents the results os work performed during the first two years of a program of investigation into the corona- and insulation-related performance of high-voltage direct-current (HVDC) transmission lines. The ultimate objective of the program is the preparation of a HVDC transmission line design reference book. Towards this end, the research to date has included tests on two different conductor geometries (one at +- 120KV, the other at +- 800KV) on a bipolar test line to evaluate the audible noise,radio interference, corona loss, electric field and ion performance of different line geometries. In the area of insulation, the research has concentrated on the investigation of parameters which influence the flashover strehgth of contaminated insulators of air gaps. Although the existing base of information is not sufficient to generate reliable design guidelines, possible approaches to the development of such guidelines are described, and some tentative calculation techniques are suggested.