Tall fescue (Festuca arundinacea Schreb.) is a versatile perennial grass. Often referred to simply as "fescue," it is easy to establish, tolerant of a wide range of management regimens and a good forage yielder. Laboratory nutritive analyses of fescue compare favorably to those of other cool-season grasses. Fescue was first planted on a widespread basis in the U.S. in the 1940's, and now occupies some 35 million acres in the Eastern half of the country. Since the discovery in the late 1970's that an endophyte (fungus) within this grass affects both grazing animals and the grass itself, attitudes toward fescue have changed greatly. This publication provides a review of current knowledge of the effects of endophyte-infected (EI), as compared to endophyte-free (EF) fescue and explains options livestock producers have for using this_important grass.