Many U.S. residents who speak little English may face language barriers when seeking health care. This article describes what is currently known about language barriers in health care and outlines a research agenda based on mismatches between the current state of knowledge of language barriers and what health care stakeholders need to know. Three broad areas needing more research are discussed: the ways in which language barriers affect health and health care, the efficacy of linguistic access service interventions, and the costs of language barriers and efforts to overcome them. In each of these areas, we outline specific research questions and recommendations.