The U.S. Supreme Court's Atkins v. Virginia (2002) decision exempted capital defendants with intellectual disability (ID) from execution. In its decision, the U.S. Supreme Court asked states to generally conform to clinical standards. However, states vary greatly on legal definitions of ID and capital procedures, such as standard of proof. When states use a standard of proof of ID that is higher than the lowest, capital defendants with ID are placed at an increased risk for unlawful execution. The overarching purpose of this dissertation is to understand the policy, practice, and research implications of high standards of proof of ID for the social inclusion of persons with ID. Chapter 2 was a secondary data analysis that used publicly available records. The purpose of Chapter 2 was to explore the differences between states' death penalty statuses and standards of proof of ID across social inclusion factors. The overall findings were that states do not differ on social inclusion factors by death penalty status alone, and that states using a standard of proof higher than the lowest were less socially inclusive than states using the lower standard or no standard. Chapter 3 was a theoretically driven, single-case study that explained why Georgia remains the only state to implement the highest standard of proof. To answer this question, I conducted interviews with key informants in the public sector. I also obtained and transcribed a two-hour long legislative hearing that occurred in 2013 on Georgia's standard of proof. I used the impressionist narrative tale and constant comparative methods to develop themes and dimensions. Themes and dimensions were used to inform nine recommendations that address the lack of information or misinformation presented in the 2013 legislative hearing. Chapter 4 was a policy analysis that used a value-critical approach to examine the standard of proof of ID within Georgia's 1988 statute. I presented findings across the social history context, the judicial context, and the economic context. I then provided a justification for the recommendation to clinically evaluate death row inmates in Georgia for ID.