Fuzzy Ergo Sum is a science fiction novel written during 2006-2009 by Wolfgang Diehr as a sequel to H. Beam Piper's Fuzzy trilogy: Little Fuzzy, Fuzzy Sapiens, and Fuzzies and Other People. The trilogy concerns the discovery of a primitive species of small, childlike but sapient furry creatures on Zarathustra?, a frontier planet with valuable mineral deposits, and the subsequent conflicts this generates between the Fuzzies, the humans who befriend them, and those who would exploit the Fuzzies and their land.
Fuzzy Ergo Sum begins shortly after the conclusion of the trilogy, involving characters from those books in further adventures and conflicts.
Things have been quiet on Zarathustra-maybe too quiet-for the Colonial Government, Jack Holloway, the Fuzzies and the Charterless Zarathustra Company for the last couple of years. Baby Fuzzy made his first kill, the sunstone agreement with the CZC has kept the planetary government in the black and the Fuzzies and humans peacefully co-exist in a nearly symbiotic relationship.
All is well until several men arrive on Zarathustra with an agenda that will spell trouble for humans and Fuzzies alike. In a very short period, the Chief Colonial Prosecutor is abducted, a dangerous criminal escapes from prison and a major stockholder with a blood vendetta digs into the company's records.
The story ends in a cliffhanger, and is concluded in Diehr's Caveat Fuzzy.
The first edition includes a few words of the Fuzzies' language invented by Ardath Mayhar for her own Fuzzy book, Golden Dream: A Fuzzy Odyssey. Although Diehr had obtained permission for use from Mayhar, a protest over copyright was issued by her publisher, Ace Books. In response, Diehr rewrote the relevant passages, and a second edition was issued three months after the first.