As nations strive to achieve and sustain universal health coverage (UHC), they seek answers as to what health system structures are more effective in managing health expenditure inflation. A fundamental macro-level choice a nation has to make is whether to adopt a single- or a multiple-payer health system. Using Taiwan's National Health Insurance (NHI) as a case, this paper examines how a single-payer system manages its health expenditure growth and draws lessons for other countries whose socioeconomic development is similar to Taiwan's. Our analyses show that as a single payer, Taiwan's NHI is able to exercise its monopsony power to manage its health expenditure growth. This is achieved primarily through the adoption of a system-wide global budget. The global budget sets a hard aggregate budget cap to limit NHI's total spending to its expected revenue, with the annual budget growth rate established by a process of negotiation among key stakeholders. The global budget system is complemented by comprehensive and continuous monitoring and review of encounter records of all providers and patients, enabled by the NHI's advanced information technology. However, by paying its providers using a point-based fee schedule, Taiwan's NHI suffers from inefficient service provision. In particular, providers have incentives to increase use of services and drugs with positive profit margins. Furthermore, Taiwan demonstrates that its control of NHI expenditure growth might be leading it to inadequately meet the changing needs of the population, resulting in the rapid growth of private insurance to cover services excluded or not fully covered by the NHI. If this trend persists and results in a two-tier system, Taiwan's NHI may risk compromising the equity it has achieved in the past two decades.