This study investigated the rate of success for IT projects using agile and standard project management methodologies. Any successful project requires use of project methodology. Specifically, large projects require formal project management methodologies or models, which establish a blueprint of processes and project planning activities. This study asked what methodologies should be utilized to improve the chances of project success, as project managers are engaged in decision making. A deficiency in reliability and consistency correlate to a lower success rate of projects. The objective of this quantitative study was to relate the use of the agile or waterfall methodologies and specific critical success factors (CSFs) to IT project success for a sample of IT project managers who have used these methodologies. The results of the analysis of variance showed that there were significant differences between the extent of use of effective communications, user involvement, and use of a quality plan between the models. The results of the Pearson's correlation test showed that project success is significantly and positively associated with effective communication, user involvement, and use of a quality plan in the agile methodology. In addition, the results of the Pearson's correlation test showed that project success is significantly and positively associated with only effective communication and use of a quality plan in the waterfall methodology. Lastly, the results of multiple linear regression analysis showed that none of the CSFs of effective communication, use of quality plan, and user involvement significantly influences the success of the project in both the agile and waterfall project management models. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]