["Human Resource Development Quarterly, EarlyView. ", "\nABSTRACT\nThis study proposes and tests a curvilinear effect of job insecurity on work engagement, while also examining the moderating roles of employment contract type (permanent vs. temporary) and trait negative affectivity on this relationship. Utilizing two waves of time‐lagged data from a sample of 397 participants (273 permanent and 124 temporary employees) in Taiwan, the results reveal a U‐shaped association between job insecurity and work engagement, with contract type and trait negative affectivity moderating this association. Specifically, for temporary employees or those with high trait negative affectivity, the relationship follows a U‐shaped pattern, indicating stronger curvilinear effects. In contrast, for permanent employees or individuals with low trait negative affectivity, the association is initially negative but levels off and becomes statistically nonsignificant beyond the inflection point, suggesting a plateauing trend rather than a pronounced curvilinear effect. This study contributes to the job insecurity literature by offering a more nuanced understanding of the conditions that shape this curvilinear relationship. Additionally, this study offers practical insights for organizations by underscoring the need to tailor engagement strategies to different employee groups, such as providing support to temporary workers and individuals with high trait negative affectivity, to sustain work engagement under uncertain employment conditions.\n"]