Older employees are often stereotyped at work (e.g., as less competent, less flexible and less trainable; Posthuma & Campion, 2009). Encountering stereotypes in the workplace can make them susceptible to age-based stereotype threat, or the concern about confirming or being reduced to a negative stereotype (Steele, 1997). Although consequences of age-based stereotype threat have been identified (e.g., poorer job attitudes, greater intentions to quit; (Kulik et al., 2016; Oliveira & Cabral-Cardoso, 2018; von Hippel et al., 2013; 2019), far less is known about workplace triggers of stereotype threat or underlying mechanisms of the effect. My aim in this thesis is to identify factors that lead to stereotype threat. Specifically, I aim to: (a) identify workplace antecedent events of age-based stereotype threat and the frequency at which employees experience them, (b) explore age salience as a mediator explaining why experiencing antecedent events might lead to stereotype threat, and (c)investigate the impact of organizational-level factors on feelings of stereotype threat. This thesis comprises three main empirical chapters. In Chapter 2, I explore a broad list of workplace factors that were likely to be interpreted though an age-based lens (e.g., being overlooked for training opportunities). Across two cross-sectional studies, there were ten key factors that related to older employees’ feelings of stereotype threat. I found initial support for age salience as a mediator, such that each potential antecedent event was associated with increased age salience, which in turn, related to greater feelings of stereotype threat. To test the causal relationship between the potential antecedent events, age salience and stereotype threat, I experimentally manipulated the presence of three antecedent events using short videos. I found that experiencing the antecedent events led to increased age salience and greater feelings of stereotype threat. In Chapter 3, I explored whether organizational-level factors could predict age-based stereotype threat. To do so, I collected multi-source and multi-level data (from the younger co-workers and HR representatives of each participating organization from Chapter 2). Specifically, I explored whether being surrounded by younger co-workers who endorse age-based stereotypes was associated with older employees’ feelings of stereotype threat. I also explored the impact of formal HR policies and practices on feelings of stereotype threat. There was a marginal effect of age-friendly HR practices, indicating that having more age-friendly HR policies may be beneficial to older employees. However, in general, none of the organizational-level factors were strong predictors of stereotype threat. Finally, in Chapter 4, I present a daily diary study that investigated the frequency at which each antecedent event occurs in the workplace and whether their accumulation has an appreciable impact on stereotype threat. The results revealed that experiencing more antecedent events on a given day was associated with greater feelings of stereotype threat that day, and this relationship was partially mediated by the extent to which the antecedent event increased age salience. The cross-lagged effects showed that participants who experienced more antecedent events on a given day were more likely to experience greater stereotype threat on the following day. However, these effects were reciprocal, such that participants who experienced more stereotype threat on a given day were also more likely to report experiencing antecedent events on the following day.