Boundary objects help collaborators create shared meaning and coordinate their work across differences. Acknowledging the complex dynamics of such processes, we propose a multimodal alternative to studies’ traditionally static view of boundary objects and ask: How do boundary objects “shape-shift”? How do they emerge in varying forms across visual, verbal, and embodied modes, and in what ways does this “shape-shifting” affect meaning-making? Adopting a “strong” multimodal lens, we show how boundary objects expand in form as collaborative work proceeds through shifting shapes both across and within modes. We also show how they contract over time, reemerging exclusively in some and not other shapes, often in simplified forms. These dynamics both enable and constrain meaning-making. Expanding shapes of the boundary object allow collaborators to develop rich shared understandings. Contracting shapes, in turn, condense meaning-making into efficient communication among those familiarized with the object, yet obscure meaning-making for newcomers who cannot make sense of its contracted shapes. Our study sheds new light on boundary objects’ multimodal nature and demonstrates how objects’ shifting shapes affect meaning-making. More generally, we offer a rich empirical account of how modes enmesh in practice, unveiling their processual and inseparable complexion.