Since the passage of the National Historic Preservation Act of 1966, State Historic Preservation Offices have been required to create and implement Statewide Historic Preservation Plans on a recurring cycle. Despite this longstanding requirement, State Plans have been overlooked in academic research and there have been few comprehensive evaluations of the planning process, the written plans, and their implementation. This thesis begins to fill that gap in research and suggests further areas of study for future researchers. Through interviews with staff at the National Park Service, an online survey of SHPOs in U.S. states, territories, and Freely Associated States, and follow up interviews with seven states, this thesis analyzes current practices of State Planning, including common challenges to planning, areas of success, and innovative practices. This thesis recommends best practices for SHPOs’ creation and implementation of Statewide Historic Preservation Plans, as well as ways for the NPS to assist states in their planning processes.