Job insecurity as an occupational stressor has been influencing the well-being of employees for some decades. Most of the studies have acknowledged the detrimental impact of this stressor on employees and organizations. Job insecurity can be divided into quantitative and qualitative job insecurity. Quantitative job insecurity is the overall concern of an employee toward the continued existence of his/her job in the future. Qualitative job insecurity is the concern of employees about losing valuable characteristics of their job in the future. In this Ph.D. thesis we attempt to replicate the impact of job insecurity on a wide range of well-being related outcomes across Iran, Belgium and the U.S. Also, we explore how the cognitive appraisals of job insecurity, namely hindrance and challenge appraisals, and employee’s attitudes such as boundaryless career orientation moderate the association between job insecurity and these outcomes. To achieve the above goals, this thesis consists of five chapters and five studies in which the association between both job insecurity and various well-being related outcomes are discussed. Chapter I is a general introduction on the studied outcomes, moderators, samples, and theories used in this thesis. Also, this chapter presents some information about the five studies in more detail. Chapter II includes study 1 and 2. In these two studies, we investigate the association between quantitative job insecurity and two popular well-being related outcomes in Belgium and Iran. Moreover, in this chapter, we test the extent to which cognitive appraisals of job insecurity can affect the association between quantitative job insecurity and these outcomes. Chapter III includes only study 3. In this study, we detect the association between qualitative job insecurity and two categorizations of well-being related outcomes, namely psychological outcomes, and behavioral outcomes, in Iran. Chapter IV contains study 4 and 5. In these two studies, we attempt to replicate the negative association between ...