Failure to learn from past mistakes and successes has consistently been a major obstacle to improving IT project management. IT Project Management: Lessons Learned from Project Retrospectives 1999-2020 addresses this shortcoming by integrating, updating, and extending the research findings from four previous studies on IT project retrospectives. The result is a "meta-retrospective" of 264 IT projects analyzed as part of a program of action research conducted between 1999 and 2020. When viewed individually, each retrospective tells a unique story and provides a rich understanding of the project management practices taken within a specific context during a particular timeframe. When viewed as a whole, these 264 projects provide an incredible opportunity to understand project management practices at a more macro level and to generate findings that can be generalized across a wide spectrum of applications and organizations.