Cryogenic electron microscopy (cryo-EM) is a revolutionary technology for making 3D images of the inner workings of cells in much higher resolution than ever possible before. Under development for four decades, it’s seen such rapid progress over the past few years that three of its developers were awarded a Nobel prize in 2017. “Cryo” refers to the fact that samples are flash-frozen before being “photographed” from multiple angles with focused electron beams. The reconstructed images show how atoms are arranged within molecular machines inside our cells – from the proton channels that help keep cells healthy by controlling their acidity to the molecular gadgets viruses use to maintain their ability to infect. This lecture presents newly obtained images that show a wide variety of these tiny engines in action, and describe cryo-EM’s potential for improving human health.