The article reviews the literature on health numeracy, the ability to understand and use numerical information, and its impact on cognition, health behaviors, and medical outcomes. Despite the abundance of health information available, many people lack basic numerical skills essential for maintaining health and making informed medical decisions. Low numeracy distorts risk perceptions, reduces medication compliance, impairs access to treatments, and negatively affects medical outcomes. It also increases susceptibility to extraneous factors and biases in judgment and decision-making. The review outlines four theoretical approaches to numeracy and discusses their implications for understanding and improving numeracy. The authors emphasize the need for theory-driven research to address the gap between the availability of health information and the public's ability to process it effectively. National and international surveys show that a significant portion of the population lacks basic numerical skills, which is particularly concerning given the increasing complexity of health-related numerical information. The article also reviews specific instruments used to assess health numeracy and highlights the limitations of current measures. Overall, the review underscores the importance of improving numeracy to enhance informed decision-making in healthcare.The article reviews the literature on health numeracy, the ability to understand and use numerical information, and its impact on cognition, health behaviors, and medical outcomes. Despite the abundance of health information available, many people lack basic numerical skills essential for maintaining health and making informed medical decisions. Low numeracy distorts risk perceptions, reduces medication compliance, impairs access to treatments, and negatively affects medical outcomes. It also increases susceptibility to extraneous factors and biases in judgment and decision-making. The review outlines four theoretical approaches to numeracy and discusses their implications for understanding and improving numeracy. The authors emphasize the need for theory-driven research to address the gap between the availability of health information and the public's ability to process it effectively. National and international surveys show that a significant portion of the population lacks basic numerical skills, which is particularly concerning given the increasing complexity of health-related numerical information. The article also reviews specific instruments used to assess health numeracy and highlights the limitations of current measures. Overall, the review underscores the importance of improving numeracy to enhance informed decision-making in healthcare.