Accelerating gradient is one of the crucial parameters affecting the design, construction, cost, and energy reach of the next generation linear accelerators. The main phenomenon that limits the gradient of rf linacs is vacuum rf breakdown. I present recent R&D efforts directed toward increasing the operating gradients of normal conducting accelerating structures. This work includes study of the basic physics of rf breakdown phenomena and novel methods of building the accelerating structures. The study of the basic physics includes high power tests of short X-band accelerating cavities at room and cryogenic temperatures, and high gradient tests of mm-wave accelerating structures. Novel methods of manufacturing include precision milling of full scale accelerating structures and use of new materials such as hard copper-silver alloy.