Turbulence not just affects our well-being during flights; it also plays a central role in nature and in technology: it influences how pollutants spread in the atmosphere, how efficiently fuel and air mix up in combustion motors, and it limits the transport of liquids in pipelines, to give just a few examples. As a result, researchers have been trying for over a hundred years to better understand how turbulence first arises. Scientists now describe, for the first time, how a fully turbulent flow arises in pipe and square duct flows.