This chapter explores the many species of ants, order Hymenoptera, family Formicidae, which invade turfgrass areas throughout the United States. The subfamily Formicinae includes many ants found on turf. The fire ants are by far the most important and common pest ants of turfgrass in the southeastern states. Ants are primarily troublesome in turfgrass areas because they build mounds as they form subterranean homes for their colonies. They seek out drier, well-drained sandy soils that have low water-holding capacity. The galleries they form, which damage roots, add to the desiccation of the soil, and the turf in the surrounding areas becomes thin and unsightly. Mounds of various sizes and shapes, formed according to the habits of the ant species, are often detrimental to mower blades. The chapter then looks at the red imported fire ant, the turfgrass ant, and the harvester ant.