The paper presents a discussion on some of the engineering studies performed to determine the design parameters of the Itaipu convertor stations. The following studies are discussed: steady-state conditions, reactive-power compensation, insulation co-ordination and arrester protective scheme, current stresses, system stability, main characteristics of the master control, AC and DC filter and DC line resonance. For each of these study areas, the paper gives a summary of the study methodology used, indicates the main study results, and includes some of the system problems encountered and the solution adopted.