Multiparty collaboration is particularly challenging in large-scale enterprise integration (EI) implementations as diverse organizational subunits and external consultants need to work together to enact transformational change. We argue from prior research that a boundary organization -- a formal organizational space that enables participants with divergent interests to collaborate -- provides a relatively durable structure to manage emergent tensions and conflicts among stakeholders in EI projects. To better understand how a boundary organization enables ongoing, dynamic, multiparty collaboration, we introduce the concept of boundary organization practices to describe practices enacted as part of the boundary organization to define the working rules and arrangements for diverse stakeholders to work together.We conducted a longitudinal exploratory case study of a multiyear EI implementation in a large logistics organization. Our analysis of the longitudinal data led us to identify three sets of boundary organization practices (i.e., organizing to negotiate, to contain, and to sustain). These sets of practices emerged to address the divergence that arose in each of the three phases (designing, realizing, and leveraging) of EI implementation. We also find artifacts to be an integral part of the boundary organization practices as they motivated, coordinated, and enabled collaboration among diverse stakeholders.