The problem of generated waste as a result of the implementation of construction projects, has  been aggravated recently because of construction activity experienced by the world, especially Iraq, which is going through a period of reconstruction, where construction waste represents (20-40%) of the total generated waste and has a negative effect on the environment and economic side of the project. In addition, the rate of consumpted  amounts of natural resources are estimated to be about 40% in the construction industry, so it became necessary to reduce waste and to be manage well. This study aims to identify the key factors affecting waste management through the various phases of the project, and this is accomplished by using the Delphi technique. After conducting three questionnaire rounds of the Delphi to a group of experts, the results of this study identified forty four key factors affecting waste management distributed on the phases of the project, where found that the factor of frequent errors in the designs has the highest effect on the design phase, and the factor of the use of construction techniques that do not generate waste has highest effect on the construction phase. The purpose is to provide data base for decision-makers to control waste management well to avoid all affecting factors, with the possibility of building waste management system based on factors effective for each phase.