The most important single invention in the Industrial Revolution was the steam engine. Not only did it produce unprecedented levels of power for machinery, it was capable of producing power a distance from the source of energy, the coal mines. In addition, being itself portable led to a revolution in transportation, both on land and at sea.
The first practical steam engines were developed in the 17th century and employed pumping water from mines. The Newcomen engine improved on the design around 1712 but was still inefficient. James Watt improved the efficiency and showed how to convert linear to rotary motion, making steam engines much more practical for powering machinery.
Steam engines are driven by external combustion. They were replaced as the primary source of power for machinery by the development of electrical power and for transportation by improvements in internal combustion engines, such as gasoline-powered and diesel engines.