In 2002, the Bill & Melinda Gates Foundation started the Early College High School Initiative (ECHSI). Through this initiative, more than 200 Early College Schools (ECSs) opened by fall 2009. All of the schools aim to provide underserved students access to college classes while in high school. This article will provide an overview of the first 6 years of the ECHSI, and key findings across 5 years of the ECHSI evaluation, in particular highlighting how participants have implemented the ECHSI's core principles. However, the ECS is not a rigid model, and this article describes the variations in ECS implementation. Finally, this article documents outcomes such as attendance, grade-to-grade progression and graduation rates, student performance on assessments, and college credit accrual. (Contains 1 table, 1 figure, and 12 footnotes.)