This Technical Report provides general guidance on the electromagnetic environment issues of HVDC transmission lines. It concerns the major parameters adopted to describe the electromagnetic environment of a High-Voltage Direct Current (HVDC) transmission line@ including electric fields@ ion current@ magnetic fields radio interference@ and audible noise generated as a consequence of such effects. Engineers in different countries can refer to this Technical Report to: - ensure the safe operation of HVDC transmission lines@ - limit the influence on the environment within acceptable ranges@ and - optimize engineering costs.