Mathematicians, with some exceptions, have not described what it means to practice and use mathematics ethically. This has contributed to a culture permissive of data-related scandals, questionable professional practices, and decreased public trust in science. By integrating ethical reasoning (ER) into undergraduate mathematics classes, the mathematics community can begin to alter the perception that, if mathematics features abstract and theoretical constructs, then the mathematics practitioner has no ethical responsibility. Considering the ‘mathematics practitioner’ to be both the user of, and the contributor to, mathematics, this proposal seeks to establish ER as a regular component of mathematical practice. Rather than wait until practitioners have committed to a career in research, this project target instructors of, and students in, math courses (such as Calculus, Differential Equations, and Linear Algebra) that are foundational for diverse STEM fields and seek to introduce a learnable, improvable skill set (ER). <br/><br/>The project builds on a published, developmental model of ethical reasoning and a national survey of mathematics practitioners’ perceptions of aspects of ethical practice that were derived from mathematics, statistics, and computing (the results of which we refer to as the “proto-guidelines”) Using this foundation, the project seeks to foster integrity in both the use of, and contribution to, mathematics. The project will invite interested participants to a workshop in Year 1 to develop learning outcomes featuring ER in their respective mathematics course contexts and to draft supportive teaching materials. Throughout Year 2, participants will share their work with stakeholders, including non-instructor stakeholders through focus groups with business, industry, and government about their perceptions of building ER capabilities in users of, and contributors to, mathematics. This input will be useful in formulating authentic problems that instructors can use and refine. In Year 3, participants will attend national and regional workshops where instructors of other foundational mathematics courses, and at different student levels, can adapt the tested ER instruction materials to promote implementation among a broader set of learners. Data collected will include survey data from materials implementation, qualitative data related to the development and implementation of the materials, and surveys and interviews of project stakeholders. Data will be analyzed using a Qualified Change algorithm. This project serves the national interest in the faith and trust the public puts in the results of STEM research, including both that which is part of mathematics and that which involves the use of mathematics.<br/><br/>This project is jointly funded by the Improving Undergraduate STEM Education and Ethical and Responsible Research Programs.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.