The choice of an excavation support system (ESS) is an important decision, that has a significant impact on the project cost, schedule, and safety. In this decision, numerous critical factors must be considered, however not enough information are available in this early phase of the project. This study aims to determine the crucial factors and their relative weight during the selection process, to provide the decision-maker with a solid base to compare between ESS and overcome the lack of knowledge in this early project phase. Therefore, a literature review was carried out to identify the most critical factors, then a questionnaire was distributed to set the relative weight of these factors during the selection of an ESS. Finally, 6 case studies were used to justify and retrofit these findings.