Cardiorenal syndrome (CRS) represents a complex and increasingly prevalent clinical entity characterized by bidirectional interactions between cardiac and renal dysfunction, in which impairment of one organ accelerates injury to the other. From an epidemiological perspective, CRS reflects the convergence of two major global epidemics: heart failure and chronic kidney disease (CKD), both of which are rising sharply due to population ageing, improved survival from acute cardiovascular events, and the expanding burden of metabolic disease. Large population-based studies demonstrate that up to half of patients with chronic heart failure have concomitant CKD, while cardiovascular disease remains the leading cause of mortality in advanced CKD. Although precise quantification of CRS remains challenging due to heterogeneous definitions, evolving diagnostic criteria, and inconsistent coding practices, convergent evidence from heart failure, CKD, acute kidney injury, and dialysis registries confirms that CRS is common, prognostically severe, and resource-intensive. The prevalence and incidence of CRS vary across its five recognized subtypes, with chronic phenotypes accounting for the largest global burden. Importantly, CRS is associated with markedly increased mortality, frequent hospitalizations, prolonged length of stay, and substantial healthcare costs. Understanding the epidemiology of CRS is therefore essential for clinical decision-making, health-system planning, and public health policy. Improved surveillance, standardized definitions, and integrated cardio-renal care models are critical to mitigating the growing global impact of CRS.