Reflection is a systematic process of reviewing memories. Reflection on past positive and negative memories increases well-being, as does reflection that is mediated by technology to provide rich digital records of past personal experiences. Technology mediated reflection (TMR) is rapidly growing in popularity, with many deployed systems, however we know little about how one’s mood when using TMR might influence well-being. I use theories of memory and emotion-regulation to motivate hypotheses about the relationship between reflection, mood, and well-being when using technology. I developed a web-based application called MoodAdaptor to test these hypotheses. MoodAdaptor prompted participants to reflect on positive or negative memories depending on current mood. I evaluated how mood and memory interact during written reflection and measured effects on well-being. Qualitative and quantitative data were collected via surveys, logfiles, and interviews. Follow-up assessments were also administered three months after the initial month-long study to measure potential long-term benefits. When participants reflected on memories with valences opposite to their current mood, their mood became more neutral. However this did not impact overall well-being. My findings also clarify underlying TMR mechanisms, showing that moods and memories competed with each other. When positive moods prevailed over negative memories, people demonstrated classic mechanisms shown in prior work to influence well-being. When negative moods prevailed over positive memories, memories became negatively tainted. My results have implications for new well-being interventions and technologies that capitalize on the interconnectedness of memory and emotion.