It has been long known that groups of adults learn and enact their learning in certain ways; what is little known is how groups learn and how they develop in cognitive complexity. This dissertation proposes a theory of group cognitive development by arguing that intentional adult groups are complex and dynamic, and that they have the potential to evolve over time. Groups are complex in that they are made up of individuals within different orders of consciousness (Kegan), and they are dynamic in that different orders of consciousness interact and conflict (Lonergan) during the formation and enactment of group vision, values, and procedures. Dynamic complexity theory of group development as it is referred to in this study is grounded in Robert Kegan’s constructive developmental theory and in Bernard Lonergan’s transcendental method. While both Kegan and Lonergan attend to the growth of individuals, their theories are adapted to groups in order to understand the cognitive complexity of groups, intragroup and intergroup conflict, and the mental complexity of leader curriculum. This theory is applied to two case studies, one from antiquity in the case of the first century Corinthian community engaged in conflict with its founder, St. Paul, and in one contemporary study of American Catholic parishioners engaged in contentious dialogue with diocesan leaders from 1994 to 2004. The parish groups experienced a series of dialogues during a ten year period over the issues of parish restructuring and the priest sexual abuse crisis yielding cumulative and progressive changes in perspective-taking, responsibility-taking, and in group capacity to respond to and engage local and institutional authority figures. Group development is observed against a pedagogical backdrop that represents a mismatch between group complexity and leader expectations. In Corinth, Paul’s curriculum was significantly beyond the mental capacity of the community. In the case of Catholic parishioners the curriculum of diocesan leaders was beneath the mental capacities of most of the groups studied. It is proposed that individuals sharing the same order of consciousness, understood as cognitive constituencies, are in a dynamic relationship with other cognitive constituencies in the group that interact within an object-subject dialectic and an agency-communion dialectic. The first describes and explains the evolving cognitive complexity of group knowing, how the group does its knowing, and what it knows when it is doing it (the epistemologies of the group). This dialectic has implications for how intentional groups might be the critical factor for understanding individual growth. The second dialectic describes and explains the changing relationship between group agency, which is enacted either instrumentally or ideologically; and group communion, which is enacted ideationally. The agency-communion dialectic is held in an unstable balance in the knowing, identity, and mission of groups. With implications for the fields of adult education and learning organizations, dynamic complexity theory of group development notes predictable stages of group evolution as each cognitive constituency evolves, and notes the significance of internal and external conflict for exposing the presence of different ways of knowing and for challenging the group toward cognitive growth.