In this chapter, the authors focus on issues of validity in measuring student learning as a prospective indicator of institutional effectiveness. Other chapters in this volume include reference to specific approaches to measuring student learning for accountability purposes, such as through standardized tests, authentic samples of student work, and student growth in such areas as leadership, teamwork, citizenship, and global awareness. Here, the authors consider the core issue behind the meaning and usefulness of any such measures: validity. They begin this exploration by reviewing the evolving concept of measurement validity and the role of constructs in establishing validity. They then consider how these constructs apply to student learning as a measure of institutional effectiveness. They further critique some of the current and proposed measurement practices, examining explicit and implicit constructs and the impact of common operational problems on validity, such as sampling bias and other statistical artifacts. Finally, they offer a set of standards for establishing and assessing the validity of such accountability measures. (Contains 1 table.)