Health literacy is the degree to which individuals can obtain, process, understand, and communicate about health-related information needed to make informed health decisions and is an important factor in patient health outcomes and resulting health care costs. Because of its importance across many areas of health, specific attention has been given to studying and measuring health literacy in recent years; however, the field lacks consensus on how health literacy should be defined and measured. As a result, numerous definitions and measures of health literacy exist. This fragmentation and inconsistency creates a barrier to conceptualizing, measuring, and understanding health literacy across health domains and fields. A directed literature search reveals a substantial body of work on health literacy; however, findings from studies often emphasize health literacy within specific health domains, populations, contexts, and languages, which makes the comparison of findings across studies difficult. While there is recognition that the measurement of health literacy should be improved, it is important to take into consideration what can be gained from a general health literacy focus and how this could be applied across domains.