This dissertation is three-fold. As for Chapter 1, a recent rapid-automation movement has been displacing routine labor and has sparked a series of discussion about taxation on automation such as a robot tax. However, the government's dilemma is that the planner may want to tax such physical capital that displaces routine labor---for example, industrial robots---for redistributive motives but does not want to tax other physical capital that increases such workers' productivities---for instance, collaborative robots (cobots). This paper studies a novel setting of the optimal capital taxation on physical capital in which there is asymmetric information on both labor types and capital types between the planner and market. In particular, my model focuses on a two-by-two scenario where there are two types of labor (routine and non-routine labor) and two types of capital (displacing and reinstating capital). Despite asymmetric information, I find that the optimal uniform capital tax rate over different types of capital is strictly positive, as long as the solution is interior. As for Chapter 2, stable matchings in the presence of complementarities need not exist. With a canonical form of payoff functions, the conventional sufficient condition for existence substantially restricts the range of pairwise complementarity/substitutability values. This paper provides a new sufficient condition for existence on the maximal range of complementarities/substitutabilities. Our condition allows for a new class of settings that violate the conventional condition. As for Chapter 3, Daylight Saving Time (DST) is a common energy policy worldwide, yet its practice is extremely controversial for a number of reasons, the most troubling of which is its perceived, though undetermined, adverse health impact. We examine the effects of DST on the incidence and severity of acute myocardial infarction (AMI). Our novelty is to construct a counterfactual by exploiting the quasi-experimental research design offered by the unique circumstances obtaining in Indiana. Using the data on the universe of AMI cases in 2002-2012 obtained from the Indiana Department of Health, our findings suggest increased AMI admissions after the spring transition by approximately 26%, orders of magnitudes larger than previously thought.