Participatory Irrigation Management (PIM) was formally adopted in Thailand in 2004. The involvement of farmers in water management decision making is necessary to meet the implementation challenges of this initiative. As such, the research presented in this paper considered the level of farmer involvement in water management and decision making, and the lessons learned by both government officials and farmers through the implementation of PIM in Thailand to date. Data collected from document reviews and a total of 44 semistructured face-to-face and telephone interviews of public irrigation officials and farmers nationwide show that farmers possess the full potential to manage irrigation water by themselves, and that they are making important changes to governance systems for irrigation. However, they need both the opportunity and the continuing supportof public irrigation officials for success, which is currently only being partly achieved through the PIM initiative.