The Highway Safety Improvement Program (HSIP) comprises three components: planning, implementation, and evaluation. This guide focuses on the evaluation component, which provides a critical feedback loop to update processes and inform future decisions. The target audience includes safety program managers, project managers, data analysts, and researchers involved with project, countermeasure, or program evaluations, in particular HSIP evaluations. The purpose of the HSIP Evaluation Guide is to provide direction and resources to agencies that want to begin or enhance HSIP evaluation efforts. Readers will be prepared to track critical project details in support of HSIP evaluation, perform three different levels of evaluation (i.e., project, countermeasure, and program level), and use the results of HSIP evaluations to improve decisions and processes. Readers will also understand the methods, data requirements, and considerations associated with the different levels of evaluation. Examples from various States highlight noteworthy practices and the benefits of evaluation. Employing more consistent and reliable evaluation methods will support safety decision making, positively affect processes intended to reduce crashes, optimize return on investment of safety funding, and increase the effectiveness of projects and programs.