Although academic and policy interest in health system resilience has grown considerably in recent years, the empirical literature on this topic is small and predominantly focused on effects arising from single shocks. Shocks are also under-theorised in the health systems literature. This thesis helps to address these deficits through an in-depth case study on the childhood vaccination delivery system in Lebanon, a country which has experienced a series of recent shocks overlapping in time and space, including large-scale refugee influx from neighbouring Syria, COVID-19 and a multi-dimensional political and economic crisis. The thesis opens with an overview of the theoretical literature on system resilience from health and a range of other research fields, highlighting insights regarding resilience conceptualisation, assessment and measurement that are of relevance to health systems. Two empirical papers then explore how sequential shocks have affected the vaccination delivery system in Lebanon, identifying independent and interacting vulnerabilities and their effects at multiple system levels, before tracing key system responses. These papers employ qualitative system dynamics modelling (SDM), an approach that maps out causal links between variables and feedbacks contributing, in this instance, to variations in routine vaccination coverage in Lebanon over time. A third empirical paper uses qualitative, thematic analysis to identify governance factors contributing to system responses to shocks over time. Collectively, these studies identify a series of leverage points potentially amenable to intervention, including delays affecting speed of shock recognition and mobilisation of human and financial resources. They also show how resilience-promoting measures introduced following one shock can paradoxically increase vulnerability to later ones. The final study – a realist-informed systematic review – links findings from the empirical work to intervention evidence from the wider health systems literature, to inform a series of policy recommendations for supporting system resilience in Lebanon over the medium-to-long-term.