The construction industry is not performing as desired by the stakeholders that compose it. Several authors and practitioners have claimed that moving the industry towards a more integrated approach to project delivery could notoriously improve the overall performance of the industry. The main purpose of this dissertation was to obtain a unified framework for project integration, by identifying the critical success attributes for achieving project integration, the different levels of importance of attributes other than the critical success attributes to improve the integration process, and by determining if there are major differences among the perceptions of respondents depending on their role in the industry. In addition, this study also sought to identify potential associations between the integration attributes and the different project performance or project success criteria. In order to develop this framework and to identify the potential associations between integration attributes and project performance, a survey was conducted. The sample of the survey was composed of construction industry practitioners; it included owners, facility managers, engineers, specialty consultants, general contractors, subcontractors, among other professionals. The sample size was 264 respondents. The main method used for developing the framework was the Thurstone Scaling Method of Successive Interval Procedure; in addition, this method was complemented and validated using correlation analysis, factor analysis, cluster analysis and analysis of the means. According to the perception of respondents, 19 attributes out of the 45 attributes under study, were identified as critical for successfully achieving project integration. In addition, four other categories of importance were identified and the other integration attributes were categorized accordingly. No major differences were found between the perceptions that different project participants had in regard to the importance of the different attributes to achieve project integration, leading to the conclusion that the perception of respondents in regard to this matter is very homogeneous. The potential impact of the 45 attributes on 12 performance criteria was analyzed. According to the perception of respondents, most of the integration attributes have different levels of impact on the different performance criteria; however there is not a clear relationship between the level of importance for achieving project integration and the level of potential impact on the different performance criteria. Most of the integration attributes are divided in two groups depending on their behavior across all integration criteria; in addition there are three groups that have one attribute each. The potential impact of each of these groups differs from one performance criterion to the other; however there are some performance criteria where the behavior of the groups is similar. The groups have a similar behavior on cost, time, and productivity; they also behave similarly on quality and owner satisfaction; on functionality and user satisfaction; and on health and safety and environmental impact and sustainability.