In this dissertation, I study several topics in labor economics using modern causal methods. In Chapter 1, I study the labor market outcomes of World War I veterans. These veterans are distinct – unlike most who served in the army they did not initially receive large post-service benefit packages. Therefore, studying their outcomes presents a unique opportunity to understand how military service, unconfounded by benefits, affects veterans. I find that most veterans benefited from army service – long-run earnings increased. However, for a subset of veterans serving in the army was costly and employment rates declined. Chapter 2 is a joint project with Francine Blau, Lawrence Kahn and Matthew Comey. I am grateful for Fran and Larry for the opportunity to work on their idea. In the paper we study the impact of selection bias on estimates of the gender pay gap, focusing on whether the gender pay gap has fallen since 1981. Previous research has found divergent results across techniques, identification strategies, data sets, and time periods. In our project, we apply all prior research strategies to the best data available. Our main finding is that there is a large decline in the gender wage gap even after accounting for selection. However, we note that substantial gender wage gaps remain, and convergence has stopped since the 1990s. In Chapter 3, I study how students’ exposure to tenure systems affects their long-run outcomes. As contemporary variation in tenure regimes is limited, I go back to the 20th Century. This was the period where most states implemented tenure; in 1910, only one state had a tenure regime, but by 1977 every state had a tenure law. I then exploit the passage of tenure laws between 1910-1977 in a difference-in-differences design. Event study models reveal that tenure systems negatively impact student outcomes, but only when they improve teachers’ job security. However, most tenure laws do not affect students because they do not affect teacher job security. Most laws don’t affect teachers because they are implemented during a teacher shortage. In a shortage, market forces already protect most teachers from dismissals.