Advancing health literacy (HL) research requires high-quality HL measures. This chapter provides an overview of the state of the science of HL measurement: where the field started, currently is, and should be going. It is divided into eight key sections looking at (1) the history of HL measurement, (2) the relationship between HL definitions and measurement, (3) the HL conceptual domains most and least frequently measured, (4) the methods used to validate HL measures, (5) the characteristics of the participants in the measurement validation studies, (6) the practical considerations related to administering HL measures, (7) the advantages and disadvantages of using objective versus subjective HL measures, and (8) future directions for HL measurement.

Based on the material presented in this chapter, the following conclusions can be drawn. First, there is an enormous proliferation of HL measures and this growth presents both opportunities and challenges for the field. Second, to move the field forward, there is an urgent need to better align HL measurement with definitions of HL. Third, some HL domains, such as numeracy, are measured more often than others, such as speaking and listening. Consequently, it is important to think about novel mechanisms to measure HL domains that are rarely measured. Fourth, HL measures are most often developed, validated, and refined using classical measurement approaches. However, strong empirical and practical rationales suggest making an assertive shift toward using modern measurement approaches. Fifth, most HL measures are not well validated for use in minority populations; consequently, future validation studies should be mindful of validation samples. Sixth, HL measures can be administered using multiple modes, most frequently via paper-and-pencil surveys. Identifying which mode of administration is most suitable requires reflecting on the underlying measurement purpose and the characteristics of the participants being measured. These considerations should also be made when deciding between a subjective versus objective HL measure.

Cumulatively, this chapter provides tools to help readers select and use the most appropriate measures of HL for their needs. It also provides rationale and strategies for moving the science of HL measurement forward.