The aim of this project is to contribute to and stimulate the growing body of academic work being carried out within the Blue Humanities by developing a 'poetics' of the twenty-first century sea. The thesis defines these poetics as the accurate representation of present-day and near-future marine environments, validated through reference to their manifold contemporary expressions: physical reality, news reporting, and (critical) theory, but also fiction, film, installation, music, painting, poetry, and sound recording. The forward-looking aspect of the thesis ultimately results in the outline for a model for cross-species saltwater cohabitation: the ‘multispecies marine society’. The discussion begins by revisiting such concepts as ‘society’, ‘citizen’, and ‘culture’ in the context of a new critical appreciation of the shared physicality of human beings and non-human marine beings and environments. The thesis builds on these findings to demonstrate the value of situating the totality of marine actors in a network configuration. Following this reappraisal of the modern seascape, the project draws on the work of a number of key authors – Stacy Alaimo, Karen Barad, Donna Haraway, Bruno Latour, and Anna L. Tsing – to describe the world-building, or sea-defining powers of storytelling. It also establishes the importance of key ecofeminist principles in recalibrating the relationship between humanity and the sea, and calls for acts of remembrance and reconciliation with respect to past and present injustices inflicted by humans on non- and more-than-human marine others. Finally, the validity of the concept of multispecies marine society is tested through juxtaposition with the stark reality of ongoing environmental degradation; it is found that cross-species saltwater ‘becoming’ holds promise no matter the circumstances, and today more than ever before. This helps the thesis maintain a pragmatic view of the disappearance of familiar seascapes: in their place comes a multispecies ferment of possibility.