The environmental impact assessment (EIA) system often critiqued because 'of its failure to provide adequate stakeholder and public involvement during the assessment process of development projects. This thesis contributes to this EIA debate by investigating the limitations of, challenges to effective SP, within the context of Oman, to provide a better understanding of these limitations to support the environmental decision-making process. This study design adopts a multi-methods-based exploratory approach, combining methods from both quantitative and qualitative strategies. Data were collected through policy and other documents, semi-structured interviews, and Q sorting technique for rich information that help in achieving the research aim and objectives. Guided by the 'interpretive' approach, qualitative data were analysed through thematic analysis approach, whereas quantitative data (Q sorts) were analysed statistically through factor analysis. These methods enabled greater understanding of limitations and challenges to effective SP in EIA to be identified, described and discussed through policy and practice implications. This thesis has identified three main findings. First, SP in EIA is principally influenced by national policy guidelines. Political, socio-economic contexts play a crucial role in the environmental decision-making process, and hence strongly impact the policy of SP in EIA process. For Oman, the lack of an explicit policy of participation in EIA was found as one major challenge to effective SP in EIA. Second, the empirical investigation findings show several non-policy factors that influence SP in EIA. Of the most important, is the recognized traditional communication and representation systems that exist within a conservative Islamic community, as is the case of Oman. Thirdly the use of Q-Method demonstrates that the challenges to effective SP in EIA are attributed to latent influential factors that exist among various key actors of decision and policy-makers. These are often tacit control powers that indirectly influence policy-making as well as practice. The extent to which these tacit powers control the policy making process in \ various contexts might be an interesting field for further research.