<p>Health professional mobility has become a defining feature of 21st-century health systems, highlighting deep structural inequalities within global health labour markets. International movement of health workers can unfairly disadvantage source countries by losing publicly funded training investments, although it offers benefits at both individual and system levels. This narrative review compiles evidence on current patterns, drivers, and impacts of health worker migration, and explores the emerging idea of proportionate co-investment as a framework for fairer global health workforce management. Literature was gathered through database searches of PubMed, Scopus, Google Scholar, and major organisational and government websites. Evidence was presented following SANRA guidelines. The review emphasises dominant South–North migration flows. Widening wage gaps, poor working conditions, and power imbalances allow high-income countries to benefit from “implicit subsidies” in health workforce development. For source countries, this results in service gaps, poor distribution, higher health system costs, and slower progress toward universal health coverage. Current ethical recruitment codes and bilateral agreements are mostly voluntary, fragmented, and inadequate to fix labour-market imbalances. Proportionate co-investment redefines health worker migration as a shared global duty. Destination countries should systematically support health workforce education, retention, and working conditions in source countries. This review advocates a proactive framework grounded in proportionality, predictability, system alignment, and shared governance, drawing on emerging models such as skills partnerships and destination-country financing. Embedding proportionate co-investment could shift global policy from managing health worker losses to sharing responsibilities, promoting ethical mobility, and strengthening health systems worldwide.</p>