This thesis is basically concerned with the status of the 'regional development processes' under the system of 'medium-term national socio-economic development planning'. The evaluation of the regional dimension of the sectoralised approach to elaboration of the national plan in a centralised system of planning is the core of the concern. It represents both the explicit contribution of 'reflective practice' and of a systematic survey of 'room for manoeuvre' experienced by a professional planner working in a planning agency - the Plan and Budget Organisation of the Islamic Republic of Iran - at the national level in the field of regional planning. The thesis provides the reader with an original exposure detailed mechanism of 'doing planning' ' from the inside of planning process', discusses the normative and positive ingredients of planning practice - theoretical, technical, procedural, instrumental, and organisational - and examines the following hypotheses: -the conventional approach of elaboration of the national plan neglects the regional dimension and spatial analysis of its choices; -the conventional system of planning prevents both implementation of the deliberate regional policies and incorporation of the results of the independent regional development studies into the national planning process; This dissertation introduces the planning system in Iran, reviews ten efforts at medium-term socio-economic development plans, analyses the regional policies of these plans, and classifies various schools of thought in Iranian regional planning. It concludes that the national planning process would have a haphazard and chaotic contribution in the processes of regional development . Finally recommends an alternative approach to elaboration of the national plan with more satisfactory consideration of both sectoral and regional development' criteria. Finally the dissertation offers a proposal for a sectoral-regional approach of elaboration of a national plan, on the basis of empirical and theoretical analysis of the regional efficiencies of the Iranian national plans and planning procedure.