Here are some of his most famous works:
Series:
* Paratime: This series features a universe where different timelines exist and can be accessed through the "paratime" process.
* "Paratime" (1946): The first story in the series, introducing the concept of paratime.
* "Little Fuzzy" (1962): A classic story about the ethics of contact with an alien species.
* "Fuzzy Sapiens" (1964): The sequel to "Little Fuzzy," focusing on the legal battle to protect the Fuzzies' rights.
* "The Other Side of the See-Saw" (1965): A short story that explores the consequences of paratime interference.
* The Terro-Human: This series explores a world where humans and Terros (a telepathic race) coexist.
* "Space Viking" (1952): The first novel in the series, introducing the Terros and their relationship with humanity.
* "Lord Kalvan of Otherwhen" (1964): A sequel to "Space Viking," featuring Kalvan as a leader in a war against the Terro.
* The Podkayne of Mars: This series follows the adventures of a young woman traveling the solar system.
* "Podkayne of Mars" (1963): The first novel in the series, introducing Podkayne and her adventures.
* "The Cosmic Computer" (1967): A later book in the series, featuring Podkayne and her involvement with the Cosmic Computer.
Standalone Novels:
* "The Genesis of the Earth" (1951): An early novel that explores the origin of life on Earth.
* "The Last Day" (1956): A thriller about a group of scientists struggling to survive a nuclear war.
Short stories:
* "Omnilingual" (1957): A classic story about the invention of a device that can translate any language.
* "The Last Legion" (1966): A story about a group of survivors fighting to rebuild civilization after a global war.
Piper's work is often characterized by its sharp wit, strong characters, and thought-provoking themes. He is considered one of the pioneers of science fiction, and his stories continue to be popular today.