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 <italic>expand</italic> in form as collaborative work proceeds through shifting shapes both across and within modes. We also show how they <italic>contract</italic> 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.