This document summarizes and analyzes past literature on blended learning. It begins by defining blended learning and discussing early attempts from 1999-2002 that combined online and face-to-face learning. A definition period from 2003-2006 saw increased research and definitions of blended learning, including the highly cited definition by Garrison and Kanuka that blended learning thoughtfully integrates classroom and online experiences. The document analyzes 28 highly cited works to reflect on the past, present, and future of blended learning research.