Construction delays are common in construction industry and create major concerns for project performance. Construction delays are caused by many factors. The aim of this paper is to identify delay factors on construction projects and analyze these factors with the relative importance index method. For this purpose, 83 different delay factors were identified, categorized into nine major groups, and visualized by the Ishikawa (fishbone) diagram through detailed literature review and interviews with experts from the construction industry. The relative importances of these delay factors were quantified by the relative importance index method. The ranking of the factors and groups were demonstrated according to their importance level on delay. According to the case study results, the factors and groups contributing the most to delays (those needing attention) were discussed, and some recommendations were made to minimize and control delays in construction projects. DOI: 10.1061/(ASCE)ME.1943-5479.0000129. (C) 2013 American Society of Civil Engineers.