In this longitudinal field study, we examine reciprocal relationships between within-person changes in cognitive appraisals (threat and challenge) and work engagement across an organizational merger. Examination of these cyclical relationships provides a more accurate understanding of the complexity of employees’ experience of change and a new test of spiraling work engagement and cognitive appraisals. Latent change score modeling is used to analyze three waves of longitudinal survey data (N=623). Our findings showed that engagement mitigated threat appraisals and enhanced challenge appraisals through pre- and post-merger phases. A reciprocal relationship from threat appraisal to engagement was also found, such that threat fueled decreases in engagement throughout the merger. Challenge appraisal was associated with enhanced work engagement during the first merger phase. By examining the dynamic relationships over time among these critical psychological processes, this study contributes to research including change appraisals, work engagement, organizational change, and broaden-and-build theory.