The assessment landscape is varied and complex. Because assessments serve many purposes, they can take multiple forms depending on what they are measuring and how they are used. The intended purpose behind each assessment influences its design, and the design influences how assessment data can be used by students and their families, school, district and state leaders. State and district policymakers have important decisions to make about when and how to gather and use assessment data across K-12 education systems, but federal policy is a key component of every state's assessment system. This report discusses how the Every Student Succeeds Act (ESSA) lays the foundation for state summative assessment systems and requires state education agencies to implement statewide assessments. In addition to federal compliance requirements, states may use assessment data in separate state accountability systems or opt to administer certain assessments to better inform policymaking and priorities.