This chapter presents a discussion and findings of health literacy and its relevance to health informatics. We argue that the Internet represents an increasingly important vehicle for knowledge translation to consumers of health information. However, much of the Internet-based information available to consumers is difficult to understand by those who need it the most. A critical factor to improve the comprehensibility, and therefore the quality, of health information is literacy. We summarize studies of various aspects of health literacy, such as readability and comprehensibility of risk information. We also point out ways in which the study of health literacy, including prose and numeric literacy, should inform researchers, health practitioners, and Web designers of specific ways in which consumer health information can be improved.