The longer life expectancy combined with decreasing birth rates in many developed countries has led to a growing awareness of the need for older adults to extend their working lives. As more people reach their 80s and 90s, working into their late 60s and 70s will become more common for social, mental engagement, and economic reasons. However, opportunities and conditions for older adults to continue working today are fraught with challenges across individual, organizational, and societal levels. This study aims to contribute to the current body of knowledge on longevity in the workplace by bringing forward the voices of older workers in their 60s and beyond and exploring the complex factors that influence their motivation to continue to work through a systems perspective. Using a mixed-methods research approach grounded in self-determination theory (SDT), this study reveals a multilevel set of factors that influence the work motivation of older adults. The findings demonstrate that beyond older workers' fundamental need for financial security, physical stamina, and mental cognition, they also have four key psychological needs: purpose, autonomy, competence, and relatedness. Older adults with high intrinsic motivation are found to be more likely to work longer than those with extrinsic or introjected motivations. Furthermore, the mindset of older workers, shaped by both their growing awareness of the finite nature of time and their internalized beliefs and values over decades of lived experiences, influences their motivation to work. Factors in their everyday circle and societal conditions such as their home situation, workplace environment, and government-sponsored retirement benefit programs also affect the satisfaction or frustration of their psychological needs and, consequently, their motivation to continue to work beyond the traditional retirement age. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]