Centaurea cyanus, commonly known as cornflower or bachelor's button (among other names), is an annual flowering plant in the family Asteraceae native to Europe. In the past, it often grew as a weed in cornfields (in the broad sense of "corn", referring to grains, such as wheat, barley, rye, or oats), hence its name.

C. cyanus is now endangered in its native habitat by agricultural intensification, particularly by over-use of herbicides. However, it is now also naturalized in many other parts of the world, including North America and parts of Australia.