What is Transmedia? The Transmedia Cultures companion demonstrates that transmedia, and indeed transmedia storytelling, are fundamental to the human experience of being in the world and creating the stories of who we are, both as individuals and communities. Transmedia is not just limited to the Star Wars or Harry Potter franchises nor narratives exclusive to new media platforms and devices, though both these areas will necessarily be discussed. Indeed, transmedia embraces a multiplicity of media platforms (old and new, online and offline), content expansion, and evolving forms of audience engagement. This collection of concise, readable essays takes a holistic approach, expanding the areas of everyday life implicated in transmedia worldbuilding and the levels of immersion that they, purposely or otherwise, create. Beginning with a comprehensive introduction and historical overview, the volume explores contemporary transmedia worlds like Buffy the Vampire Slayer, The Walking Dead, Life is Strange and BTS Universe as well as urgent topics such as COVID-19, Black Lives Matter, and human rights on the internet. User-created worlds (Magic: A Gathering) and ones that express individual identities (Queerskins) are also of particular interest. This volume offers a fresh approach to transmedia cultures, revealing the ever-increasing levels of entanglement they have within our real lives and with those we experience in other more imaginative or creative ones, bringing into focus exactly what is at stake in the «worlds» we choose to call our own.