This dissertation consists of three essays in the areas of labor economics. The first essay investigates how competition shapes peer effects. Competition is widely used to motivate efforts and increase performance. However, in many domains, performance is aided by cooperation between agents in addition to their own efforts. In this case, competition may impose costs on cooperation since the chance of winning is decreasing in the success of peers. Education is a natural setting where peer interactions and help from others enhance individual performance. This paper uses administrative data from a university in China to examine how competition changes peer effects and peer interactions. Exploiting randomly assigned roommates, we find that high-ability students have detrimental effects on their high-ability roommates' academic performance. More importantly, this negative peer effect increases significantly along multiple competition intensity dimensions within a dorm room. The follow-up survey we conduct reveals that this is likely driven by competition discouraging help and interactions among roommates. In the second essay, my co-authors and I study how religious practices affect worker performance. More than six billion people practice certain religions. How religious practices affect worker performance is theoretically ambiguous. On the one hand, religious practices require time that is then unavailable for production. Moreover, certain practices, such as fasting, may also directly impact worker productivity. On the other hand, religion may foster a better work ethic and workers may find ways to attenuate the potential economic costs. Our paper examines the effects of religious practices on labor supply and productivity and how workers respond to a change of external constraints in the context of observing Ramadan fasting. We obtain high-frequency administrative data from a large retail chain in Indonesia and utilize an event-study approach to compare the performance of Muslim salespersons and their non-Muslim colleagues during Ramadan. We find that Muslim salespersons leave work 22 minutes earlier, and their productivity (after controlling for demand side changes) decreases by 21% around sunset, compared to their non-Muslim counterparts. Meanwhile, they exert more effort earlier in the day to compensate for decreased productivity later in the day or shorter working hours. Due to their reallocation of efforts, there is no significant change in the aggregate daily sales of Muslim salespersons during Ramadan. Lastly, we find that such effort reallocation is more salient among workers with more Ramadan experience in the workplace, suggesting this optimization is learned over time. The third essay reexamines the impacts of China's One-Child Policy (OCP) on aggregate fertility. We compare fertility in two provinces with the OCP, Guangdong and Fujian, with demographically similar bordering regions without the OCP, Hong Kong and Taiwan. Using micro-census data, these paired case comparisons show that the OCP did not decrease aggregate fertility, measured as birth likelihood and average number of siblings. Using data from cities in two other provinces, we also show the OCP was likely not binding on fertility levels because relaxing the OCP did not increase fertility rates in pilot cities compared to neighboring cities that did not relax the policy. Our findings emphasize the need to understand the limits of policy to affect national-level fertility rates.