Education practitioners, researchers, and policymakers are increasingly focusing on social and emotional learning and development and positive school climates as essential factors to establish equitable learning environments in which all young people can thrive. The purpose of this guide is to assist states and districts in making decisions about which types of measures related to social and emotional learning and development and/ or school climate to use, how those measures could be used, and important factors to consider in the process. In developing this tool, Council of Chief State School Officers (CCSSO) and EducationCounsel interviewed and consulted with researchers, practitioners, and other subject matter experts and conducted a literature review of resources and tools in the field. Given the many resources and experts in social and emotional learning, school climate, and measurement, this tool serves as a guide for states that are navigating these decisions by sharing: (1) key principles related to selecting and using these measures; (2) the benefits and challenges of using different measures; (3) the purposes for which different measures may be appropriate to use; and (4) key resources to dig deeper in relevant areas. For survey measures (school climate and social and emotional competencies), this guide also provides key questions to ask in selecting survey instruments and some "do's and don'ts" for selection and implementation.