Purpose: How does a small business engage in boundary work to innovate its business model towards sustainability? We employ a boundary work lens to trace the endeavors of a small company to explore, negotiate and (re)align organizational boundaries in its multi-stakeholder network around new, sustainable value propositions. Design/Methodology/Approach: We engaged in longitudinal research of a company's endeavors for multi-stakeholder alignment in sustainable business model innovation (SBMI). By means of thick description, this paper offers rich empirical insights on the processes of interaction between a small company and its stakeholders in the Dutch pork sector, with special attention to boundary spanners, boundary objects and the mutual organizational boundary changes. Findings: We find that the shaping and shifting of organizational boundaries highly influences the process and content of the business model innovation. During the phases of boundary exploration, brokering and boundary changes, there is a pivotal role for boundary objects to deal with uncertainties, to facilitate strategic discussions and to find solutions to different valuation frames, power tensions and role divisions between stakeholders. Research implications: SBMI can benefit from boundary work, as it helps companies to find value opportunities in the organizational boundaries of their external stakeholders, addressing challenges that emerge from existing organizational boundaries, and establishing boundary arrangements to facilitate this process. Originality/Value: Boundary work interlinks concepts of identity, power, competences and efficiency in entrepreneurial processes of collaborative SBMI. The framework and methods of this study further our understanding of the co-evolutionary processes of SBMI. [ABSTRACT FROM AUTHOR]