As courts in separation-of-powers systems are said to have the power of neither the purse nor the sword, their institutional legitimacy is essential for ensuring compliance with their decisions. While institutional legitimacy has been examined in-depth for national high courts, the legitimacy of sub-national courts has been overlooked. In this dissertation I develop a new measure of court-level institutional legitimacy for state high courts. I use multilevel regression and poststratification to create state-level measures from individual-level survey results. In this dissertation, I develop a theory of review and delegation by state high courts. I argue that these courts work toward two main goals: implementing their policy preferences and maintaining the legitimacy of their institution. I argue for a two-stage process that considers whether or not the court will decide on the constitutionality of a statute in the first stage and whether they will overturn the statute and delegate policy control back to the other branches of government in the second. Relying on the literatures on both institutional legitimacy and political delegation, I suggest that courts may delegate policy control back to the other branches of government by specifically stating this in their opinion. Finally, I examine the conditions under which a state high court will delegate to either the state legislature or the executive branch. Overall, I find that legitimacy is important when considering state high court decision-making; and it must be considered along with political context and institutional rules as one of the central motivations for state high courts in separation of powers theories.