The focus of this chapter is on how to design science assessment items that are linked to the content standards in Benchmarks for Science Literacy and the National Science Education Standards. This chapter describes (1) the authors’ criteria for determining that the assessment items test the targeted ideas and not some other ideas, (2) precautions we take to ensure that each assessment item is a fair and accurate measure of student knowledge, and (3) the use the authors make of student feedback during item development rather than relying solely on psychometric features to judge the suitability of the items.