The Department of Aeronautics and Astronautics at the Massachusetts Institute of Technology is designing a portfolio assessment system to assess students' achievement of program outcomes. In the past three years, the undergraduate aerospace engineering program has embarked upon major curriculum reform initiatives centered on 16 program outcomes detailed in its CDIO Syllabus. Portfolios will be organized into categories reflecting these outcomes. (The 16 CDIO skills, or program outcomes, are also the cornerstone of the program's self-study report for ABET accreditation.) This paper addresses the planning and development of portfolios for assessing students' achievement at the end of their programs in aerospace engineering at MIT. Background In its strategic plan of 1998, the Department of Aeronautics and Astronautics at the Massachusetts Institute of Technology (MIT) committed to major reform of its curriculum, teaching and learning methods, and laboratory environments. To achieve its goals, the department framed its curriculum to model a product system life cycle. The four phases in the curriculum are referred to as Conceive-Design-Implement-Operate (CDIO). The Conceive stage includes defining the need and technology, considering the enterprise strategy and regulations, developing the concept, architecture, and business case. The second stage, Design, focuses on creating the design, i.e., the plans, drawings, and algorithms that describe what will be implemented. Implement refers to the transformation of the design into the product, including manufacturing, coding, test and validation. The final stage, Operate, uses the implemented product to deliver the intended value, including maintaining, evolving and retiring the system. Curriculum reform efforts centered on a set of 16 key learning outcomes deemed essential for new engineers. (See Table 1) These outcomes, categorized as technical, personal, interpersonal, and CDIO system skills, were validated in surveys of faculty, students, alumni, and industrial representatives, both in the United States and in Sweden. They serve as the program outcomes of MIT's two aerospace education programs accredited by ABET under its new evaluation criteria and policies. 1 The more detailed list of outcomes, called the CDIO Syllabus, is available at the CDIO Web-site. 2 Here, the 16 program outcomes are outlined in two additional levels of detail.