A new taxonomy for describing and defining medication adherence has been proposed to address the lack of uniformity in terminology used to describe deviations from prescribed therapies. The study aimed to develop a conceptual framework based on behavioral and pharmacological science, supporting quantifiable parameters. A systematic review of literature from 1976 to 2009 identified over 10 terms describing medication-taking behavior, often with differing meanings. The new taxonomy distinguishes between processes ('Adherence to medications', 'Management of adherence') and disciplines ('Adherence-related sciences'). 'Adherence to medications' is divided into three phases: initiation, implementation, and discontinuation. The taxonomy also defines 'non-adherence' as occurring during initiation, implementation, or early discontinuation. The proposed terminology aims to promote consistency and quantification in research and clinical practice. The taxonomy was developed through a European consensus meeting involving 80 participants from 13 countries, resulting in a unified framework. The new taxonomy includes definitions for terms such as 'adherence', 'compliance', 'concordance', and 'persistence', and emphasizes the importance of clear, consistent definitions for accurate measurement and analysis. The study highlights the need for a standardized approach to medication adherence terminology to improve clinical outcomes and health policy decisions.A new taxonomy for describing and defining medication adherence has been proposed to address the lack of uniformity in terminology used to describe deviations from prescribed therapies. The study aimed to develop a conceptual framework based on behavioral and pharmacological science, supporting quantifiable parameters. A systematic review of literature from 1976 to 2009 identified over 10 terms describing medication-taking behavior, often with differing meanings. The new taxonomy distinguishes between processes ('Adherence to medications', 'Management of adherence') and disciplines ('Adherence-related sciences'). 'Adherence to medications' is divided into three phases: initiation, implementation, and discontinuation. The taxonomy also defines 'non-adherence' as occurring during initiation, implementation, or early discontinuation. The proposed terminology aims to promote consistency and quantification in research and clinical practice. The taxonomy was developed through a European consensus meeting involving 80 participants from 13 countries, resulting in a unified framework. The new taxonomy includes definitions for terms such as 'adherence', 'compliance', 'concordance', and 'persistence', and emphasizes the importance of clear, consistent definitions for accurate measurement and analysis. The study highlights the need for a standardized approach to medication adherence terminology to improve clinical outcomes and health policy decisions.