Proficiency in science is being defined through performance expectations that intertwine science practices, cross-cutting concepts, and core content knowledge. These descriptions of what it means to know and do science pose challenges for assessment design and use, whether at the classroom instructional level or the system level for monitoring the progress of science education. There are systematic ways to approach assessment development that can address design challenges, as well as examples of the application of such principles in science assessment. This Review considers challenges and opportunities that exist for design and use of assessments that can support science teaching and learning consistent with a contemporary view of what it means to be proficient in science.