There are several key questions related to health literacy that have not been systematically studied, both internationally and in Slovenia. Among other things, the project provides a concise review of health literacy research in Slovenia. We also analyze previous studies on the relationship between health literacy and vaccination, along with explanatory mechanisms (mediators) of this relationship. Additionally, we offer an in-depth look at one dimension of health literacy—critical health literacy—and its impact on vaccination and vaccination attitudes. We conducted the first empirical study in Slovenia on the relationship between critical health literacy and parental hesitancy towards childhood vaccines in Slovenia, as well as the explanatory role of vaccine knowledge. The project also addresses the issue of the validity and reliability of the health literacy measurement tool HLS-EU-Q16 among Slovenian adolescents, adults, and the elderly. Furthermore, we validate the vaccine-related health literacy among parents and individuals without children, thereby examining the suitability of the health literacy measurement tool for these target groups as well. The project also provides a review of interventional studies aimed at increasing health literacy and positive vaccination attitudes, vaccination coverage, and the effectiveness of public health interventions and measures to increase vaccination coverage in Europe and worldwide. Additionally, we analyze the legal regulations regarding vaccination and their effects on vaccination coverage and trust in vaccination in Europe and globally. Based on the project’s results, we offer recommendations for improving health literacy and vaccination coverage in Slovenia and worldwide.