This paper synthesizes the literatures on labor dynamics and urban growth and agglomeration by presenting new evidence on the micro-level establishment dynamics of metropolitan areas. I explore how the patterns of job reallocation and entry and exit affect the growth and composition of these areas. I find that high-growth metropolitan areas have high rates of job and establishment turnover, primarily though higher rates of gross job creation and establishment entry, and have a relatively young distribution of establishments. Variations in the age distribution and differences in the entry and exit patterns of young establishments account for a sizeable portion of regional differences in labor dynamics and growth, even after controlling for regional differences in industry composition. These results suggest that variations in the age distribution and the dynamics that lead to such variations are important factors in understanding urban growth and agglomeration.