Compared with traditional online courses, Massive Open Online Courses (MOOCs) are larger in scale, distributed worldwide, clear of financial barriers, and without geographic constraints. MOOCs provide an opportunity to teach interesting or critical content to new groups of learners who may not otherwise have the chance to receive high-quality education. As such, MOOCs have inspired rethinking and innovation in university education. Tens of thousands of enrolled students create a disruptive scale factor that raises both new possibilities and challenges, while inviting new visions and agendas. Although MOOCs have been broadly recognized and are considered to be an innovation in online education, researchers and practitioners have little understanding of (1) what the best practices are for students, instructors, or even MOOC carriers because of the newness of the MOOC paradigm, (2) how to improve student retention given the high dropout rate and (3) how to better support MOOC instructors to help them produce more attractive MOOCs. To better understand and address these issues, I apply mixed methods -- interviews and various sorts of log data analysis -- to characterize distinctive students' and instructors' motivations, perceptions, challenges and activity patterns during learning/teaching in MOOCs. Based on this richer understanding, I use scenario based design method to identify and present instructional and platform design implications for the next generation of MOOCs. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]