Abstract: Personal task management (PTM) is a common human activity that is supported by a plethora of dedicated e-PTM tools. Yet, little is known about how and why PTM behaviors change over time, and how PTM tools can accommodate such changes. We studied changes in 178 participants' PTM behaviors in a survey to inform the design of personalizable e-PTM tools that can accommodate changes over time. In follow-up interviews with 12 of the survey respondents, we deepened our understanding of the changes reported in the survey. Based on the reasons behind the reported changes, we identified factors that contributed to changes in PTM behaviors: changing needs, dissatisfaction caused by unmet needs, and opportunities revealing unnoticed needs. Grounded in our findings, we offer implications for design of PTM tools that support changes in behaviors as well as implications for future PTM research.