This report describes the process of developing and validating the enhanced ACT. The report describes the changes made to the test content and the processes by which these design decisions were implemented. The authors describe how they shared the overall scope of the enhancements, including the initial blueprints, with external expert panels, resulting in feedback on and iterative updates to the blueprints and proposed changes. With the revised blueprints in place, the authors then focused on collecting data from multiple sources and stakeholders to support decisions about the use of new and altered item types. The report describes evidence collected from multiple cognitive laboratory studies conducted with students; these studies support both the cognitive processes associated with item and passage types continuing from the legacy ACT and the validity of the item- and passage-level enhancements in particular. The authors present statistical evidence that demonstrates continued reliability and validity of the enhanced ACT. The goal of this document is to provide transparency to stakeholders about the decisions made throughout the design process, as well as to document supporting evidence collected for each change.