The concept of project-based learning (PBL) has garnered wide support among a number of K-12 education policy advocates and funders. PBL is viewed as an approach that enables students to develop the "21st century competencies"--cognitive and socioemotional skills--needed for success in college and careers. This issue focus, pulling from a recent MDRC working paper, "Project-Based Learning: A Literature Review" (ED578933), defines project-based learning, describes how it works and what it takes to implement PBL, and provides recommendations for advancing research on PBL's design principles, effectiveness, and implementation.