Political scientists typically view unilateral action as the president “going it alone” in opposition to Congress. However, implementation of unilateral action relies on the cooperation of administrative agencies. In this dissertation, comprising three papers, I start with this premise that unilateral actions should be considered acts of delegation. First, I conceptualize delegation and discretion for the executive branch context and provide novel measures of those concepts to facilitate empirical research. I then turn to applying these measures to empirical questions, studying both potential determinants of variation in delegation and discretion, and consequences of this variation for inter-branch politics.The first paper, “The Administrative Politics of Unilateral Action: Measuring Delegation and Discretion in the Executive Branch,” introduces novel measures of executive-branch delegation— the extent of agents’ authorization for action—and discretion—the flexibility offered to agents in defining how to use that authority. The paper provides evidence of the reliability and validity of these measures, which are substantive and rely on textual analysis rather than structural proxies. The main contribution of the paper is the introduction of the Administrative Delegation Dataset, which provides scores for 1,641 presidential unilateral directives; including executive orders, memos, and proclamations; issued between 1936 and 2021. To my knowledge this is the first such measure of executive-branch delegation, and it promises to be a useful tool for researchers of executive-branch politics.In the second paper, “Delegation by Executive Order: Discretionary Windows in Presidential Unilateralism,” I leverage these new scores to consider the president’s ability to constrain bureaucratic behavior in the context of executive orders. In particular, I examine the relationship between the role of agencies in the formulation of an executive order, and the order’s associated discretionary window. The paper uses data from Rudalevige (2021), identifying the origins of more than 500 executive orders as either emanating from within the White House, or originating in executive branch agencies. Using my delegation and discretion scores, I find that agency development of an order is associated with a narrower grant of discretion relative to development by White House staff, even when controlling for order significance and extent of delegated authority. Moreover, this relationship does not seem to have changed over time, and does not appear to vary by party. This finding sheds new light on the use of discretion within the executive branch.In the final paper, “Participatory Unilateralism: Understanding Congress’s Role in Presidential Unilateral Policymaking,” I advance my principal argument: that Congressional committees can use oversight to shape the implementation of executive orders by administrative agencies. Using a dataset of 1,420 executive orders issued between 1970 and 2021, as well as all Congressional committee hearings pertaining to oversight of executive orders conducted over the date range (n = 362), I find that higher delegation and discretion scores are associated with more Congressional hearing activity. This relationship is generally not conditioned by partisan division but persists during periods of both unified and divided government. The implication is that when agents are given the authority and latitude to execute unilateral directives, Congress has an opportunity to shape the implementation of those orders through committee oversight.