This page describes the use of portfolios as an assessment tool. It is one of a series of Classroom Assessment Techniques (CATs) provided by the Field-tested Learning Assessment Guide (FLAG) website. The CATs of FLAG were constructed as a resource for science, technology, engineering and mathematics instructors to emphasize deeper levels of learning and to give instructors valuable feedback during a course. This site provides an overview of what portfolios are, how and when to use them, and why they are useful for assessing student understanding. The site is also linked to a set of discipline-specific "tools" that can be downloaded for immediate use, as well as supplementary links and sources to further explore this assessment tool.