The purpose of the paper is to analyse the role of valuation in the property investment decision making process and to propose a new methodology to manage decision making process for development processes in urban renewal and redevelopment. The starting point is the failure of traditional tools to manage information and uncertainty in the decision making process. A new methodology provides a more environmentally valid representation of decision making behaviour and suggests the use of scenario as a tool to manage the uncertainty. The methodology suggests a model to manage the decision making process: the problem framing, the stage of scenario building, and the phase of problem solving. The problem framing is concerning with the development of the problem space. The stage of scenario building is concerned with the phase of scenario plots and the final scenarios description. The valuation and the definition of scenario strategies is the last step of the methodology. A case study tests the methodology. The case study concerns a case of urban regeneration in Venice. The importance of this case study is the actual interest of owners, developers and Public administration to start a redevelopment process. The methodology is applied to a real decision making process with the support of parties involved in the process.