Transparent electrodes, indespensible in displays and solar cells, are currently dominated by indium tin oxide (ITO) Films although the high price of indium, brittleness of Films, and high vacuum deposition are limiting their applications Recently, solution-processed networks of nanostructures such as carbon nanotubes (CNTs), graphene, and silver nanowires have attracted great attention as replacements A low junction resistance between nanostructures is important for decreasing the sheet resistance However, the junction resistances between CNTs and boundry resistances between graphene nanostructures are too high The aspect ratios of silver nanowires are limited to similar to 100, and silver is relatively expensive Here, we show high-performance transparent electrodes with copper nanofiber networks by a low-cost and scalable electrospinning process Copper nanofibers have ultrahigh aspect ratios of up to 100000 and fused crossing points with ultralow junction resistances, which result in high transmitance at low sheet resistance, e g, 90% at 50 Omega/sq The copper nanofiber networks also show great flexibility and stretchabilty Organic solar cells using copper nanowire networks as transparent electrodes have a power efficiency of 3 0%, comparable to devices made with ITO electrodes