In the United States, the labor market participation rate of older workers aged 50 and above has increased, and one-third of the labor force is made up of older workers in 2020. The trend of lifetime employment with one firm has been displaced by contingent employment in the current flexible labor market. Consequently, many older workers experience frequent employment transitions until they exit the labor market completely. However, the dynamics of labor market participation among older workers, especially those experiencing repetitive unemployment and employment in older age, are not well understood.This dissertation aimed to investigate trends in employment transitions among older workers, with a focus on job search activity, job availability in the community market, and employment support program participation in a state. In Chapter 1, the historical and theoretical evolution of aging populations was discussed, with three specific periods defined in this study: the initial introduction of welfare provisions, the looming individual safety net collapse, and visualized risks and retirement insecurity. Chapter 2 utilized latent class analysis, which identified five latent classes in the patterns of job search activities among older workers from the Health and Retirement Study. Multinomial regression analysis revealed that the patterns of job search activities are significantly associated with different types of employment outcomes, in addition to individual and employment characteristics. Chapter 3 examined job availability in the local market using two datasets, including the O*NET database and the American Community Survey. The findings showed low rates of matching between job vacancies and older workers, with higher concentrations in three occupational groups among older workers despite a wide range of available occupations. Chapter 4 demonstrated that workforce development programs under the Workforce Innovation and Opportunity Act improved the employability of older female participants but not for other disadvantaged participants who were older in age or non-white individuals. This study found that commonly chosen training programs aligned well with common occupations of the older workforce throughout the state. Finally, Chapter 5 provides implications of the three studies in this dissertation and discusses future directions to improve employment transitions among older workers in the United States.