For decades, the impact of domestic livestock grazing on rangelands in the Southwest has been debated by scientists, land administrators, ranchers, those with environmental concerns, and others, but the debate has become more focused In recent years. The important ecological  questions related to grazing impacts are difficult to address because they require long-term studies and lack the control necessary to isolate the influence of different environmental  factors. This paper is based on three relatively long-term data sets, two from desert grassland in southern New Mexico (the New Mexico State University College Ranch and the Jomada Experimental Range) and one from shortgrass vegetation in south-central New Mexico (Fort Stanton). These data indicate that herbage production varied over the years under conservative cattle grazing, but exhibited no obvious downward trend for periods approaching 50 years. Herbage production declined during drought, while responding to favorable precipitation following droughts. These studies indicate that moderate cattle grazing In the Southwest is sustainable and that climate often exerts a controlling influence that can obscure other environmental influences.