Sustainability has become critically important for the success of any balanced tourism development. This cannot be achieved without full consideration and integration of sustainable development principles into the planning mechanisms of the tourist destination/s. This study was initiated to justify the role of planning as a tool for implementing sustainability in tourism. It has hypothesized that a complete evaluation of performance of the tourism planning mechanism should be considered as a starting point, highlighting the needs, strengths, weaknesses and deficiencies of tourism planning mechanisms adopted by tourist destinations. The research method proposed an assessment system for the different levels of the planning mechanism (policies, strategies, plans and techniques) from a sustainable point of view and thus contributed to the field of tourism planning assessment and evaluation. The research divided sustainability in tourism into four main dimensions: economic, environmental (natural and manmade), socio - cultural and continuity of the development process. It developed a set of key criteria to assess each dimension at every level of the planning mechanism. As Egypt was selected as a case study, the research offered an analysis of its tourism planning mechanism with a focus on points of strengths and weaknesses at each level. Primary data (face to face interviews) and secondary data (tourist policy and documented tourist plans) were employed to examine each element of sustainability. This was followed by recommendations and suggestions for enhancing the performance of Egyptian tourism planning to attain more sustainable development goals and to implement more efficient tools for the application of sustainable tourism. The research also highlighted the role of assessment and evaluation in tourism studies and the importance of conducting an ongoing assessment of tourist planning and development processes. This in turn leads to improving the functions of each planning stage, monitoring the whole planning process and controlling deviations in the planning performance. This study has directed attention towards the field of evaluation and assessment in tourism and has introduced a new path for sustainable tourism development planning.