The purpose of this study is to explore how groups decide to use asynchronous online discussion forums in a non-mandatory setting, and, after the group decision is made, how group members use online discussion forums to complete a collaborative learning project requiring complex data gathering and research processes. While a large body of research on computer-mediated communication (CMC) has documented successful intervention strategies to promote and sustain online discussion forums, little of the research has examined the use of online discussion forums in voluntarily contexts, wherein the decision to use online discussion forums is a personal decision and participation is not a graded component. This study approaches the research questions using a naturalistic case study of one graduate-level blended learning course with 55 students. Employing both student interviews and content analysis methods, this study revealed that the factors affecting the group decision to use online discussion forums are (1) successful or unsuccessful experiences during the first trial, (2) perceived affordances of CMC tools, and (3) the interplay between the nature of collaborative tasks and perceived efficiency. The content analysis of online postings in two voluntary groups revealed that when groups decided to use online discussion forums, participation levels were almost equal among individual group members, and discussion threads were sustained until the final completion of the collaborative project.