Lord Kalvan of Otherwhen

Lord Kalvan of Otherwhen is a 1965 science fiction novel by American writer H. Beam Piper; it is part of his Paratime series of stories, and was expanded by John F. Carr to form the Kalvan series (with some installments co-written by Carr and other writers). It recounts the adventures of a Pennsylvania state trooper who is accidentally transported to a more backward parallel universe. It was published posthumously, making it Piper's final science fiction novel.

The book is an expanded version of the novelettes "Gunpowder God", which had been published in the November 1964 issue of Analog Science Fiction and Fact, and "Down Styphon!", which had been published in the November 1965 issue of Analog. "Gunpowder God" itself is a Paratime-series rewrite of the unpublished story "When in the Course", which takes place in the Terro-Human Future History milieu.

A sequel, Great Kings' War, was written by Roland Green and John F. Carr. Carr further continued the storyline with the novels Kalvan Kingmaker, Siege of Tarr-Hostigos, The Fireseed Wars and the forthcoming The Gunpowder God (which shares the same title as the original novelette).