Health literacy is a composite term used to describe the capacities of persons to meet the complex demands related to health in modern society. As an outcome of health education and communication activities, it represents the cognitive and social skills that determine the motivation and ability of individuals to gain access to, understand and use information in ways that promote and maintain good health . The concept has gained increasing attention both in research and practice due to its close association to the social determinants of health , health behavior and health outcomes , health service use  and quality of health systems as well as capacity building for professionals . Along with the increasing interest in empirical work on health literacy, there has been a growing demand for tools to measure health literacy .
The existing tools that purport to measure health literacy vary in their approach and design, as well as in terms of their purpose. Some tools have been developed for the purpose of screening, and serve to divide people into categories with low or high levels of health literacy. Examples of this kind of tool are the Rapid Estimate of Adult Literacy in Medicine (REALM) [7, 8], the Test of Functional Health Literacy (TOFHLA) [9–11] and the Newest Vital Sign (NVS) . As they are often used in clinical settings, these tools are necessarily short and quick and easy to use. Other tools aim at measuring a broader concept of health literacy, with a view to provide an in-depth assessment of the dimensions of health literacy, or to explore its relationships with social determinants, health behavior, health status or healthy service use such as the National Assessment of Adult Literacy survey (NAAL) , the Critical Health Competence Test (CHC) , the Swiss Health Literacy Survey , the Health Literacy Management Scale (HeLMS)  and the Health Literacy Questionnaire (HLQ) . Furthermore, existing health literacy measurement tools differ in terms of their administration style and their focus on specific aspects, such as the recognition and pronunciation of medical terms, numeracy, comprehension, and decision-making competencies. In terms of their technical qualities, the tools differ in terms of scoring and ranges. Accordingly, the time and resources needed for application also vary [18, 19]. Yet, in spite of the wide range of tools that are available, it is recognized that many have substantial weaknesses . Existing tools are far from optimal and show several limitations . The most apparent shortcomings of most tools are that they fail to capture all relevant aspects of health literacy and only focus on one or a few dimensions of the concept; that they have a primary focus on personal attributes at the cost of population aspects; that they have an unclear relationship to current definitions and conceptual frameworks of health literacy; and that they show only weak associations with causes and outcomes of health literacy . According to Pleasant et al. , a comprehensive measure of health literacy should reflect the following attributes: build explicitly on a testable theory or conceptual framework of health literacy; be multi-dimensional in content and methodology, to reflect the emerging theories of health literacy as a construct with multiple conceptual domains and practical components; use multiple methods; distinguish health literacy clearly from communication; treat health literacy as a latent construct, in the sense that the measure should include multiple items that sample from the conceptual domains outlined by the underlying theory or conceptual framework; honor the principle of compatibility in the sense that the measure should not focus exclusively on the clinical setting to research public health behaviors and outcomes; allow comparison and/or be commensurate across contexts including culture, life course, population group, and research setting; and prioritize social research and public health applications versus clinical screening .
To accomplish the European Health Literacy Survey (HLS-EU), which aimed to measure and compare health literacy in populations in selected countries in Europe , the HLS-EU Consortium consisting of nine research institutes from Austria, Bulgaria, Germanya, Greece, Ireland, the Netherlands, Poland and Spain, developed the European Health Literacy Survey Questionnaire (HLS-EU-Q). It embraces the principles outlined by Pleasant and colleagues and captures the essential dimensions of health literacy as outlined in the definition and conceptual model proposed by Sorensen et al. .
The present paper describes the process of developing the HLS-EU-Q. Specifically, it provides a detailed outline of the structured and systematic approach that was taken concerning the item generation, pre-testing, field-testing, external consultation, plain language check, and translation of the tool, with the purpose of creating and testing a concept based, multidimensional, multinational, interdisciplinary and comprehensive measurement of health literacy in populations. As such, the paper provides insight to the extensive development process of designing the HLS-EU-Q, which is useful for its subsequent application and validation. Initially, the methods are described for each step performed in the development process. Then the results for each step are presented. Finally the development process and the attributes of the HLS-EU-Q are discussed in terms of quality and limitations.