In dual enrollment (DE), high school students are enrolled in a college course and complete all the assignments that would normally be completed as part of the course. At the end of the course, they are given a final grade on a college transcript and course credit that can be applied toward a college degree. Dual enrollment programs differ from Advanced Placement and International Baccalaureate programs in that students take college courses rather than high school courses with college-level content. DE programs vary widely in terms of how many and what college courses they offer, where the courses take place (on college or high school campuses), and who teaches them (college faculty or high school teachers who qualify as college adjuncts). This paper outlines a research overview wherein it answers the following questions: (1) What is dual enrollment?; (2) Why dual enrollment?; and (3) Who benefits from dual enrollment? (Contains 4 sources.) [For related reports, see "Implementing a Dual Enrollment Program. Guiding Questions" (ED530527) and "City College of San Francisco Academy and Pathway Dual Enrollment Program. Case Study" (ED530529).]