Thomas Newcomen developed the first truly successful steam engine, shortly after 1700. His engines were initially used for draining mines and water supply but could power machinery by putting water over a water wheel. This lecture will look at the background to the exploitation of steam as a source of power, Newcomen’s developments and how his engines worked. The lecture will move on to later improvements to the engine, particularly those of John Smeaton, and how study of the engines’ shortcomings led to James Watt making his significant contribution to steam power. Finally there is a need to explain the continuing building of Newcomen engines into the nineteenth century, long after James Watt and others produced much more powerful and economic steam engines.