BACKGROUNDEthics instruction is an important component of engineering undergraduate education, but little research has identified aspects of the undergraduate experience that contribute most to students' ethical development. Thus, an assessment of the impact of students' experiences on their ethical development is warranted. PURPOSE (HYPOTHESIS)We apply a conceptual framework to the study of engineering students' ethical development. This framework suggests that both formal curricular experiences and co-curricular experiences are related to students' ethical development. DESIGN/METHODUsing survey data collected from nearly 4,000 engineering undergraduates at 18 institutions across the U.S., we present descriptive statistics related to students' formal curricular experiences and their co-curricular experiences. Additionally, we present data for three constructs of ethical development (knowledge of ethics, ethical reasoning, and ethical behavior). RESULTSFor our sample, the quantity and quality of students' formal curricular experiences and their co-curricular experiences related to ethics was high. The levels of ethical knowledge and reasoning varied, as did ethical behavior. CONCLUSIONSOur data highlight opportunities for improving the engineering undergraduate/bachelor's level curricula in order to have a greater impact on students' ethical development. We suggest that institutions integrate ethics instruction throughout the formal curriculum, support use of varied approaches that foster high-quality experiences, and leverage both influences of co-curricular experiences and students' desires to engage in positive ethical behaviors. KEYWORDS:co-curriculum, curriculum, ethical development 470 Journal of Engineering Education 101 (July 2012) 3 INTRODUCTIONThe engineering profession requires the utmost ethical standards, and professional engineering societies across the globe are placing growing importance on ethics (e.g., Association of German Engineers, 2002; Canadian Engineering Qualifications Board, 2001; Engineers Australia, 2010; Japan Society of Civil Engineers, 1999; National Society of Professional Engineers, 2010; and Royal Academy of Engineering, n.d.). Many engineering colleges and programs consider this emphasis on ethics education to be an essential component of the undergraduate/bachelor's level curriculum (we will use the term undergraduate to refer to students pursuing a Bachelor of Science in Engineering degree), and colleges and universities have long made it a part of their missions to educate students about ethics. In fact, a recent study by the American Association of Colleges and Universities (2009) reveals that 59% of all campuses have goals related to ethical reasoning. The need to graduate engineers who have a keen sense of ethical and social implications of engineering work is further underscored in accreditation requirements. In the U.S., for example, standards established by ABET require that engineering graduates have "an understanding of professional and ethical responsibility" (ABET, ...