Multimorbidity has significant implications for public health (high healthcare utilization, increased disability and dependency, reduced quality of life, risk of postoperative complications, adverse drug reactions, etc.). People with multiple chronic conditions often require specialized care, and since a number of risk factors are common to the most prevalent chronic diseases (obesity, smoking, physical inactivity), the implications for prevention are significant. Multimorbidity is therefore an indicator of the population’s health status that complements the information provided by monitoring chronic diseases considered individually. This indicator can be useful for tailoring healthcare services (specialized consultations, care networks, etc.) and measuring the impact of the most common risk factors. Interest in measuring multimorbidity within the context of epidemiological surveillance is recent and still underdeveloped, particularly in France. The objective of this document is to synthesize the available literature on the prevalence of multimorbidity and to describe the main measurement tools. There is no consensus on the methodology to be used to estimate the prevalence of multimorbidity within the framework of epidemiological surveillance. The most widely used definition refers to the coexistence of at least two chronic diseases, without taking into account the severity or correlations between the diseases. In most studies, the prevalence of multimorbidity is estimated using self-report surveys (via interviews or self-administered questionnaires). The results obtained are highly heterogeneous. The United States, England, and Scotland use medical-administrative databases that include medical diagnoses. The Institut national de santé publique du Québec (INSPQ) is currently developing a multimorbidity surveillance system based on medical-administrative databases. In the absence of a methodological consensus, an initial objective could be to construct an indicator based on the co-occurrence of at least two or three of the major lifestyle-related chronic diseases (cardiovascular and cerebrovascular diseases, cancer, chronic obstructive pulmonary disease (COPD), and diabetes), similar to what is proposed in the United States (CDC). The Constances cohort and the Esteban survey could provide relevant information. The use of medical-administrative databases (National Inter-Regime Health Insurance Information System (Sniir-AM)) has limitations, notably the absence of medical diagnoses. However, the relevance of these data for studying multimorbidity could be explored. In any case, it seems essential to maintain scientific monitoring of this topic. (R.A.)