This dissertation focused on improving the design of online learning environments for adult learners who need and want to continue their professional development. For such a design effort to be successful, two pedagogical approaches were assumed to be especially important in enhancing online learning environments: collaborative learning and authentic tasks. Group work connects both approaches and offers great potential for learners to achieve their goals. For adult learners, group work is fundamental to an effective and meaningful learning experience because students must discuss concepts and processes as well as enact these ideas to produce a real life outcome they are likely to perform in their lives. However, the literature also addresses challenges for online learners working together to achieve common goals. Previous research emphasizes the importance of careful design for online courses employing group work. An education design research methodology was used to explore how to optimize adult learners collaborative group work in a graduate level online E-Learning Evaluation course. This two-year design research encompassed three iterative cycles of design, implementation and testing, and redesign. Data were collected from 23 graduate students and one instructor. Findings include the challenges the online groups encountered, attributes of groups working-well together and not working-well together, and the kinds of support learners needed during the group work process. Design research pursues dual goals in practice and theory. Accordingly, course components were refined to optimize students online group work experience, while at the same time, design principles were generated that can be used to support online collaborative group work in this E-learning Evaluation course, as well be applicable in other higher education online evaluation courses or courses employing collaborative group work and authentic learning tasks as their primary pedagogy. Seven design principles and 30 associated design/implementation strategies were generated and refined via three iterative cycles. These design principles to optimize group work include guidance on the following: communication, the learning community, technology, the group work process, positive interdependence, individual accountability and engagement, and individual learning.