From its founding, United States politicians and policymakers have espoused reverence for national values in the creation of US foreign policy. Yet, there are countless examples of traditional US values being disregarded in favor of interests. What are the terms of the tradeoff between US values and US interests in US foreign policy? In this dissertation I answer this question with a social-psychological theory of US foreign policy. US values are a greater determinant of US policy when these values are more connected to US national identity. I test this theory at the individual-level and at the macro-level of US foreign policy decision-making. In Chapter 2, I draw on sociological, psychological, and constructivist international relations research and assert that US national identity consists of "core" and "peripheral" values. Core values are more resilient to the challenge of interests, since disregarding them betrays central parts of US identity. Consequently, it is expected that when interests and values clash, the degree to which the interests are betrayed depends on the value's proximity to US identity. I delineate exactly which values are “core” and “peripheral” in US national identity in Chapter 3. I determine and differentiate the values associated with US national identity by analyzing the National Archives and Records Administration's "100 Milestone Documents," US federal holidays and symbols, and presidential State of the Union addresses. I find that democracy is the most privileged value in all realms analyzed. Chapter 4 proposes that an analysis of identity’s impact on policy should focus on the agents of state policy: policymakers. I also explore cognitive dissonance as a potential psychological mechanism that enforces national identity. A series of experiments show that respondents favor foreign policy actions that are consistent with US values and that respondents experience more cognitive dissonance when they are forced to argue in favor of violating US values, particularly democracy. In Chapter 5, I analyze how the tradeoff between US values and US interests occurs in US military aid policy. National values clash with national interests when policymakers are faced with the decision of whether or not to grant US military aid to countries that serve US interests but do not embody US national values. The results show that more prominent values (democracy) are almost impervious to countervailing interests while more tangential values (enterprise and human rights) exhibit wildly different effects on US military aid allocation depending on the security and economic importance of the recipient state. I discuss the results of the entire dissertation and its connection to the Trump presidency in Chapter 6.