This article outlines a “strong” theoretical approach to sustainability literacy, building on an earlier definition of strong and weak environmental literacy (Stables and Bishop 2001). The argument builds upon a specific semiotic approach to educational philosophy (sometimes called edusemiotics), to which these authors have been contributing. Here, we highlight how a view of learning that centers on embodied and multimodal communication invites bridging biosemiotics with critical media literacy, in pursuit of a strong, integrated sustainability literacy. The need for such a construal of literacy can be observed in recent scholarship on embodied cognition, education, media and bio/eco-semiotics. By (1) construing the environment as semiosic (Umwelt), and (2) replacing the notion of text with model, we develop a theory of literacy that understands learning as embodied/environmental in/across any mediality. As such, digital and multimedia learning are deemed to rest on environmental and embodied affordances. The notions of semiotic resources and affordances are also defined from these perspectives. We propose that a biosemiotics-informed approach to literacy, connecting both eco- and critical-media literacy, accompanies a much broader scope of meaning-making than has been the case in literacy studies so far.