As a geometric term, parabola suggests a narrative trajectory or story arc. In science fiction, parabolas take us from the known to the unknown. More concrete than themes, more complex than motifs, parabolas are combinations of meaningful setting, character, and action that lend themselves to endless redefinition and jazzlike improvisation. The fourteen original essays in this collection explore how the field of science fiction has developed as a complex of repetitions, influences, arguments, and broad conversations. This particular feature of the genre has been the source of much critical commentary, most notably through growing interest in the "sf megatext," a continually expanding archive of shared images, situations, plots, characters, settings, and themes found in science fiction across media. Contributors include Jane Donawerth, Terry Dowling, L. Timmel Duchamp, Rachel Haywood Ferreira, Pawel Frelik, David M. Higgins, Amy J. Ransom, John Rieder, Nicholas Ruddick, Graham Sleight, Gary K. Wolfe, and Lisa Yaszek.