This thesis assesses the determinants of farmer participation in irrigation management and the impact of participation on irrigation quality and agricultural production in the Nam Thach Han irrigation system, Vietnam. Many governments have attempted to increase farmer participation in irrigation system management through participatory irrigation management (PIM). This approach aims to reduce government financial burdens, improve the quality of irrigation management, and in turn, enhance agricultural production. However, the results of PIM have been mixed and the factors affecting its success or failure remain a topic of much debate. Using survey data from 391 households of 11 agricultural cooperatives (ACs) in the Nam Thach Han irrigation system, this study examines (i) the factors that influence farmer participation, (ii) the impact of collective action on irrigation quality (sufficiency and timeliness), and (iii) the impact of irrigation quality on rice farming technical efficiency, while controlling for environmental factors. Four main findings emerge from this thesis. We find that (i) institutional factors at the AC level such as inclusion in the PIM project, information transparency and democratic decision-making have a positive impact on participation, but sharing second-level canals between ACs reduces participation; (ii) higher participation rates are associated with a higher probability of receiving sufficient and timely irrigation; (iii) plots and households receiving sufficient water are more likely to attain higher levels of technical efficiency and; (iv) use of household-level data can provide approximately unbiased estimates of technical efficiency provided environmental factors are controlled for. This thesis provides several contributions to the literature. Participative approaches have been widely adopted in Vietnam but this is the first empirical study to use econometric models to examine the determinants of participation and the effect of collective action on irrigation quality. This is achieved using an improved set of participation indices, constructed using principal component analysis. This thesis also provides the first analysis of the effect of sufficient and timely irrigation on rice farming technical efficiency while controlling for plot-specific environmental factors.