A lawn mower is a machine that uses a revolving blade or blades to cut a lawn at an even height.

Lawn mowers employing a blade that rotates about a vertical axis are known as rotary mowers, while those employing a blade assembly that rotates about a horizontal axis are known as cylinder or reel mowers.

Many designs have been made, each suited to a particular purpose. The smallest types, pushed by a human, are suitable for small residential lawns and gardens, while larger, self-contained, ride-on mowers are suitable for large lawns, and the largest, multi-gang mowers pulled behind a tractor, are designed for large expanses of grass such as golf courses and municipal parks.

A transition from traditional hand guided or ride on mowers to automatic electric mowers is beginning to take place, with the growth in robotic lawn mower sales of 2012 being 15 times that of the traditional styles. At current rates of growth automated lawn mowers are set to soon reach the point of outselling traditional mowers in some regions.