Which event of the American Revolution is known as "the shot heard 'round the world"?

The Battle of Lexington and Concord included the "shot heard 'round the world".

The British marched toward Concord to take control of the colonial weapons. When they reached Lexington, the minutemen, knowing they were on their way (because of Paul Revere), were already there. It's still not known who fired the first shot as both sides yelled to seize fire, but a lot of people from both sides ended up dead.