Decentralized, tax-funded health systems like Italian and Spanish ones reveal relevant internal patient flows, raising concerns in terms of equity, budget imbalances, and unexploited economies of scale at the regional and organizational level. However, policymakers lack effective tools to rapidly identify the causes of patient outflows in Beveridgean healthcare systems. We address the gap by conducting a critical review of the drivers of patient mobility. Elaborating on existing knowledge, we propose a concise, versatile assessment matrix to help policymakers in understanding the most relevant causes of mobility. Specifically, we identify three main categories of drivers: insufficient service availability, poor (perceived) quality, and regulatory issues. We include appropriate indicators to identify each driver, or mix of drivers. For each of them, we also propose specific policy and organizational responses. The applicability of the model is proven by an empirical test using the Italian national hospital discharge database for all inter-regional inpatient mobility flows. In addition to adding to previous contributions on mobility drivers by creating a model that informs policymakers' understanding and actions, the paper provides an innovative approach to patient mobility by proposing a model that, for the first time, primarily focuses on the clinical discipline of the flows.