Abstract: Cryo-electron microscopy (cryo-EM) is becoming a powerful tool for determining high resolution structures of protein machineries. Its advancement and applications in structure determination are reviewed in this article. The workflow for single particle imaging is described, with an emphasis on major breakthroughs in data processing, specifically the application of Bayesian theorem in model reconstruction. Cryo-EM shows great promise in solving many more structures, and its application in in situ structure studies and protein dynamics research will expand its territory to hitherto unexplored regions of molecular biology.