Fifty years ago, NASA began a program called Project Gemini, developing deep space travel techniques and equipment to prepare for the upcoming Apollo program. Two unmanned and ten manned missions were flown, and astronauts and engineers accomplished hundreds of goals, including the first American spacewalk, a 14-day endurance test in orbit, space docking, and the highest-ever manned orbit at 1,369 km (850 mi). After the project ended in 1966, many Gemini astronauts brought their experiences with them as they went on to fly Apollo missions to the Moon. Collected here are remarkable images of Project Gemini half a century ago -- some beautiful, some technical, and a few surprisingly intimate.