Atocion armeria, commonly known as Sweet William catchfly, is a species of plant in the family Caryophyllaceae.

The name comes from the way in which small insects are trapped by the sticky sap exuded onto the stem.

Clusters of pink or lavender flowers arranged somewhat openly or compactly at the end of stems.

Stem hairless (glabrous) or slightly hairy with sticky areas, especially just below the cluster.

Has been introduced to North America and later escaped cultivation to become an invasive species.