Low literacy is a pervasive and underrecognized problem in health care. Approximately 21% of American adults are functionally illiterate, and another 27% have marginal literacy skills. Such patients may have difficulty reading and understanding discharge instructions, medication labels, patient education materials, consent forms, or health surveys. Properly assessing the literacy level of individual patients or groups may avoid problems in clinical care and research. This article reviews the use of literacy assessments, discusses their application in a variety of health care settings, and cites issues providers need to consider before testing. The authors describe informal and formal methods of screening for reading and comprehension in English and Spanish including the Rapid Estimate of Adult Literacy in Medicine, the Wide Range Achievement Test-3 , the Cloze procedure, the Test of Functional Health Literacy in Adults, and others. Practical implications and recommendations for specific use are made.