A metronome is a device, either mechanical or electronic, used to keep a steady beat for musical practice and playing. Metronomes come in a number of shapes and sizes, and most are easily set to keep different tempos.

The quest for a working metronome began roughly a century after Galileo's discoveries pertaining to pendulums. The first attempts at creating a metronome were more or less failures, due to the unreasonable lengths required to keep even the slowest of tempos, rendering fast tempos impossible.

In 1812, Dietrik Winkel was the first to begin using double-weighted pendulums to create a device very similar to modern mechanical metronomes. Johann Maelzel took these ideas and began producing a portable metronome, for which he was awarded a patent in 1816. His design is known as the Maelzel metronome. This is reflected in the standard musical notation "MM=40," which stands for Maelzel Metronome.

Originally metronomes were seen as a tool for measuring the tempo of a piece accurately; not as an aid for musicians to match a specific tempo. These early metronomes are thought by many to have been fairly inaccurate, as evidenced by the very fast speeds placed on some pieces of the time. Most famously, this is evidenced in some works of Beethoven, who began using the metronome in 1817, the year after its release.

Early metronomes were either set into motion by simply pushing the pendulum, or by utilizing a wind-up device to keep it powered for a longer period of time. Moving a small weight up or down the pendulum set the tempo either slower or faster. Once electrical apparatuses became common in the 1930s, many metronomes began using electrical pulses to keep time, often illuminating a small light to give a visual cue.

In the 1980s electronic metronomes began to become more common, allowing for more features and customization of tempo and sound. Most metronomes generate a simple 'click' at each beat, with modern metronomes also added a chiming sound at the start of each new measure. Some electronic metronomes (particularly those found on computers) allow for customization of the sounds.

Metronomes can cost as little as $15-$20 (US dollars), with feature-loaded electronic metronomes costing upwards of $150.