Public participation becomes important in the siting of a hazardous waste facility in Thailand because the public's participation can provide a variety of benefits. One item of importance is to produce an effective decision about an issue that could have a severe impact on the human community and the environment: for instance, where to site the hazardous waste facility project. Although much public participation research has been produced, very few in-depth studies are relevant to public participation and the siting of hazardous waste facilities in Thailand. It is important to study this process in Thailand because it illustrates how the process works in a non-western culture, in contrast to where most of the studies of public responses to hazardous waste facilities have been done. This study reviews the options in hazardous waste facility site selection and the public participation model for siting the hazardous waste facility. Moreover, it examines public participation in a Thai context, the barrier factors and the resulting recommendations from the case study of siting the hazardous waste facility at Ta Sit sub-district, Pluak Daeng district, Ra Yong province. The pragmatism paradigm-the combination of quantitative and qualitative methodology-was used in all steps of the study. This means the quantitative and qualitative methodology developed the research problem, and built and tested the public participation model and the barriers to public participation. An available sample was used for the pilot study; purposive sampling was used for the related government organisations, the developers, the freelance researcher, the NGO, local official leaders, and the local people who were most directly affected. Stratified non-random sampling was used for the local villagers. Data collection methods in this thesis were (a) the secondary data from the literature review, (b) the individually-delivered questionnaires from the pilot study, (c) face-to-face interviews with local people affected, (d) in-depth interviews with the main government-related organisations, the developers, the freelance researcher, the NGO, and the main local people affected, and (e) observations for general purposes. Multiple responses, frequencies and cross-tabulations analysed the face-to-face interviews; the case records analysed the in-depth interviews and field notes. The study found that in Thailand the general public was entitled to participate only at the information and the consultation levels; only the authorised decision-maker or the representative from all the stakeholders participated at the partnership level. The 17 factors that prevented the public from participating in this research were (a) the legal framework, (b) the political and institutional culture of decision making, c) conflicting resource human rights in decision making, (d) ambiguities in legislation and guidelines, (e) the pressure imposed by the project cycle, (f) time and money, (g) personal reasons, such as forgot and people had to take care of their houses, the children, the families, the patients, or even the businesses, (h) cultural differences, (i) education, (j) strong opposition, (k) mistrust, (l) physical remoteness, (m) public presentation, (n) poor presentation of the EIA findings, (o) the timing, (p) community burn out, and (q) the project size. Gender was not related to participation. Two models of public participation are used in the Thai context to increase our understanding of participation as a process and to improve decision-making effectiveness. Applications of the participation models depend upon the nature of the siting, and community responses to it. For example, in the first application, public participation at the consultation level is sufficient when the public feel safe or the acceptance conditions are satisfied. These conditions are, for example, the site is far from the community, it has on-site facilities, the public feel confident that there is no hazardous leakage or fume from the technology, there is a good monitoring programme, and, importantly, there is public trust. The opposite is true when the public feel unsafe or the acceptance conditions are not provided, as was the case in the second application. Public participation in decision making by the representatives or a referendum needs to be supported.