Long ago, in the 1920s, a conversation started in the letter columns of pulp science fiction magazines. Fans began debating what this stuff was, what it’s doing, how it’s different from other genres, why we like it so much, what we should call it, and whether robots could actually juggle. This conversation continues, and in Trace Elements: Conversations on the Project of Science Fiction and Fantasy, Jo Walton and Ada Palmer both engage with it and trace elements of it across time. These essays, written together and separately, and brought together here for the first time, consider (among other things) genre, using history in fiction, writing and disability, publication, pacing, protocols, the history of science fiction publishing, Delany, Le Guin, Yu-gi-oh, Diderot, why science fiction and fantasy might be disguised as each other, and what reading is for, no, really. As well as writing award-winning science fiction and fantasy, Ada Palmer is an intellectual historian and Jo Walton has read a lot of books. They bring this experience together in this collection of essays that are erudite, thought provoking, and also a lot of fun.