Americans seeking employment often face a conundrum: relevant work experience is a prerequisite for many jobs, but it is difficult to gain the required experience without being in the workplace. Work-based learning--activities that occur in workplaces through which youth and adults gain the knowledge, skills, and experience needed for entry or advancement in a particular career field--offers a solution to this problem. But although the benefits of work-based learning are clear, they have accrued primarily to the most highly educated and socially connected segments of the U.S. population. In recent years, educators and leaders in the workforce development field have returned again and again to the problem of providing work-based learning opportunities to the marginalized populations for whom this experience can mean the most. This paper guides the design and implementation of effective models of work-based learning that expand access for the many people who don't currently benefit from these opportunities, including the introduction of seven principles for effective work-based learning that Jobs For the Future (JFF) has identified based on more than three decades of experience in promoting and implementing education and workforce strategies that support youth and adults seeking to launch and advance in careers. [For the related document: "7 Principles for Effective Work-Based Learning," see ED567847.]