The thesis studies the political participation of Thai farmers and focuses on two main factors, namely the domestic and the external impacts, which inform the case studies of rice, sugarcane, and potato farmers groups. Overall, the research has established that farmers groups have felt the impacts of domestic factors far more strongly than external factors. Furthermore, through comparative studies in relation to the case studies of rice, sugarcane, and potato farmers groups in Thailand, differences emerged between these three Thai farmers groups, in terms of the degree to which domestic factors impacted on their political participation. The theories of Western interest groups are reviewed, in order to examine their applicability to explaining farmers groups formation in Thailand. The concepts of 'collective benefits' and 'selective incentives', which were used by Mancur Olson have been adopted as the main theoretical framework. With reference to this, the research has established that selective incentives have played a highly significant role in Thai farmers groups formation, and concludes that the problems of mobilisation, which relate to rice, sugarcane, and potato farmers groups, have been solved primarily through the provision of a range of selective incentives by the farmers groups themselves. In order to classify the differing levels of political participation of Thai farmers groups, the analytical framework provided by Grant Jordan, Darren Halpin, and William Maloney has been utilised. Accordingly, the rice and potato farmers groups are classified as 'potential pressure participants', whilst the sugarcane farmers group is classified as an 'interest group', which has enabled an examination of their political participation through the Western concept of the policy network/community framework. In order to make the Western policy network/community framework more applicable to the policy-making process in Thailand, the specific, dominant characteristics of the Thai political culture, namely the patronage system and the operation of both vote-buying and corruption are included in the analysis. This conceptual stretching does not significantly affect the original concept of the framework and the way in which it was intended to be applicable, because it already includes informal relationships such as those, which exist within the policy network/community framework. This understanding is an important aspect, which forms a part of the theoretical contribution to the discipline of international political economy and to the arena of Thai political studies. The policy network/community framework provides a new conceptual lens in the study of the political participation of Thai farmers groups. Accordingly, these arguments promote the opportunity to consider alternative frameworks in the analysis of the political participation of Thai farmers groups, and group participation across civil society more generally. The study of the political participation of Thai farmers has utilised empirical evidence, which illustrates the successes of farmers' interest groups in both Japan and the United Kingdom, in order to explain the relative successes and failures of Thai farmers. In contrast to the experiences of Western and notably Japanese farmers groups, in many respects Thai farmers are largely excluded from the policy-making process, with the only exception in Thailand being certain sugarcane farmers groups. The thesis concludes that the political participation of farmers groups in Thailand has generally been affected by domestic impacts rather than by external impacts, and that their influence in domestic policy-making has been, and is likely to remain for the foreseeable future at least, somewhat limited.