This article discusses the Pacific Northwest‐Southwest Intertie project, a program to provide electrical interconnections between the Pacific Northwest and the Pacific Southwest. When completed, the Pacific Intertie will be the largest interregional tie in North America and the first to make use of Parallel a‐c and d‐c circuits. The article discusses three modes of operation considered in the design of a high‐voltage d‐c transmission system: monopolar ‐ one pole energized, either positive or negative, with earth return; homopolar ‐ two or more poles energized with the same polarity, either positive or negative, operating in parallel with earth return; and, bipolar ‐ two poles energized, one positive, one negative, with the electrical neutral point of the rectifier and the inverter stations connected to earth. The control vault is discussed, along with intertie tests, the Western Interutility Committee, and location selection.