Portfolios are collections of student work that can be used to evaluate student abilities and improvement over time. They have several advantages, including improving cognitive abilities, enhancing awareness of thinking strategies, and promoting creativity. However, portfolios also have disadvantages, such as requiring significant time for planning, assessment, and storage. There are three main types of portfolios: documentation portfolios showcase the learning process; process portfolios emphasize reflection on the learning process; and product portfolios highlight a student's best work. Effective portfolios require planning stages where the purpose and criteria are communicated to students.