Interstate migration in the United States has decreased steadily since the 1980s, but little is known about the causes of this decline. We show that declining migration is related to a concurrent secular decline in job changing. Neither trend is primarily due to observable demographic or socioeconomic factors. Rather, we argue that the decline in job changing has caused the decline in migration. After establishing a role for the labor market in declining migration, we turn to the question of why job changing has become less frequent over the past several decades. We find little support for several explanations, including the rise of dual-career households, the decline in middle-skill jobs, occupational licensing, and the need for employees to retain health insurance. Thus, the reasons for these dual trends remain opaque and should be explored further.