The article "Defining Comorbidity: Implications for Understanding Health and Health Services" by Valderas et al. reviews the various definitions and constructs related to comorbidity, including multimorbidity, morbidity burden, and patient complexity. Comorbidity, defined as the presence of multiple diseases in an individual, is associated with worse health outcomes, more complex clinical management, and increased healthcare costs. The authors highlight the lack of consensus on the meaning of comorbidity and related constructs, which complicates research and clinical practice. They propose a more precise use of these constructs to improve understanding and management of ill health in clinical care, epidemiology, and health services planning and financing. The article discusses the nature of the conditions, their relative importance, chronology, and expanded conceptualizations, such as morbidity burden and patient complexity. It also explores the mechanisms underlying the coexistence of multiple conditions, including direct causation, associated risk factors, heterogeneity, and independence. The authors emphasize the importance of integrating these constructs to better understand and manage comorbidities, particularly in primary care and health services research.The article "Defining Comorbidity: Implications for Understanding Health and Health Services" by Valderas et al. reviews the various definitions and constructs related to comorbidity, including multimorbidity, morbidity burden, and patient complexity. Comorbidity, defined as the presence of multiple diseases in an individual, is associated with worse health outcomes, more complex clinical management, and increased healthcare costs. The authors highlight the lack of consensus on the meaning of comorbidity and related constructs, which complicates research and clinical practice. They propose a more precise use of these constructs to improve understanding and management of ill health in clinical care, epidemiology, and health services planning and financing. The article discusses the nature of the conditions, their relative importance, chronology, and expanded conceptualizations, such as morbidity burden and patient complexity. It also explores the mechanisms underlying the coexistence of multiple conditions, including direct causation, associated risk factors, heterogeneity, and independence. The authors emphasize the importance of integrating these constructs to better understand and manage comorbidities, particularly in primary care and health services research.