Learning communities are a popular strategy that community colleges nationwide have embraced in support of developmental students. In a learning community, a cohort of students takes two or more courses linked by integrated themes and assignments that are developed through ongoing faculty collaboration. While the number of learning community programs continues to grow, rigorous studies measuring their effectiveness are limited. To address this need for evidence, the Learning Communities demonstration, launched in 2007, uses random assignment to test models of learning communities at six community colleges: Kingsborough Community College, Queensborough Community College, Hillsborough Community College, Merced College, Houston Community College System, and Community College of Baltimore County. The study is designed to determine: (1) how learning communities can be designed to address the needs of academically underprepared students; (2) the effects of learning communities on student achievement, as measured by test scores, credits earned, and grades; (3) the effects of learning communities on students' persistence in higher education; and (4) what learning communities cost and how these costs compare with the costs of standard college programs for students with low basic skills. Preliminary findings will be available in 2009. This working paper describes the study's design, including a summary of the theoretical and empirical research relevant to learning communities, descriptions of the sites and their learning community models, the random assignment procedures, and plans for data analysis. (Contains 7 tables, 1 figure, and 67 notes.) [This paper was produced by the National Center for Postsecondary Research. It was written with the assistance of Oscar Cerna, Christine Sansone, and Michelle Ware.]