This dissertation studies different macroeconomic trends observed in the US labor market over the last three to four decades and understands the link between them. The first chapter focuses on understanding the decline in labor market dynamism in the US. It begins by documenting that worker mobility and wages, relative to productivity, have decreased in the US amid a rise in employer market power. It then proposes a theory of the labor market linking these trends, in which a decline in employer competition, characterized by a lower number of firms per worker, drives the decline in worker mobility and wages. The model has two main ingredients: first, there exists a finite number of employers that differ in productivity, and second, employers exert market power by excluding their offers from the set of outside options faced by their employees. The combined effect of these features, in response to a decreasing number of firms per worker, is to reduce the value of workers' outside options, thereby reducing wages and worker mobility in equilibrium. Overall, the calibrated model accounts for 2/3rd of the decline in employer-to-employer transitions rate and a fifth of the decline in wages relative to productivity from the 1980s to the 2010s. Finally, it evaluates the model's key predictions using the public-use data from the Census and documents that labor markets characterized by a lower number of firms per worker are associated with reduced measures of worker mobility and average wages. The second chapter takes a ‘measurement’ perspective to understand the decline in labor market dynamism. The starting point of the chapter is the observation that over the last four decades, employment composition has shifted towards large firms in the US. This has occurred amidst a decline in employer-to-employer transitions or external dynamism. A natural question is, are workers in large firms climbing job ladders internally rather than externally? Using data from various supplements of the Current Population Survey, it finds evidence of the prevalence of internal job ladders within large firms. It documents that job stayers in large firms, relative to small ones, realize a larger annual pay growth and a higher probability of internal job switching. Accounting for internal job ladders amplifies labor market dynamism and offsets part of the decline in external employer-to-employer switching rates. At the same time, there has been a decreasing trend in the rate of internal job switching, suggesting that the forces affecting declining external dynamism could have also had implications on internal job ladders. Finally, it hypothesizes that the decline in internal dynamism could be driven by the firm's endogenous response to decreasing labor market competition. The third chapter studies secular trends in nominal wage rigidity in the US using the 1996-00 and 2008-13 panels of the Survey of Income and Program Participation (SIPP). Using the empirical methodology of Barattieri, Basu & Gottschalk (2014), it purges measurement errors from self-reported wages by disentangling the structure breaks in individual wage series from noise. It finds evidence of, one, an increase in the frequency of wage adjustment among hourly job-stayers from 1996-2013, and two, a higher proportion of wage cuts during the Great Recession relative to the subsequent recovery. These findings are robust when the methodology is applied to salaried workers. They can be seen in light of increasing labor market flexibility in the US over the recent decades