A keynote in literature, music or public speaking is the principal underlying theme of a larger idea — a literary story, an individual musical piece or event. At political or industrial conventions and expositions, the keynote address or keynote speech is delivered to set the underlying tone and summarize the core message or most important revelation of the event. Some of the more famous keynote speeches in the United States are those at the party conventions during Democratic and Republican presidential campaigns. Keynote speakers at these events have often gained nationwide fame (or notoriety), and have occasionally influenced the course of the election: for example, Pat Buchanan at the 1992 Republican National Convention and Barack Obama at the 2004 Democratic National Convention. Similar speeches are given at political conventions and party meetings throughout the world.

Keynote speeches are also given at the graduation and commencement ceremonies of colleges, universities, and major high schools, usually by accomplished academics or celebrities invited by the student body.

The word keynote may also refer to:

• a computer software program designed by Apple Computer. See Keynote (software).