We are Patrick and Teresa Nielsen Hayden, a married couple of writers and retired editors in Tucson, Arizona. The database that starts at these two roots shows who we provisionally believe to be our (provable) ancestors, plus collateral relatives and associated lines that interest us. This database also includes ancestral lines of several friends and colleagues whose genealogy we've researched, and also some research into the ancestry of several persons important in the history of science fiction and fantasy. As of June 2026, this site contains information on over 46,000 individuals, including 493 direct ancestors of Patrick and 9,976 direct ancestors of Teresa.

Almost every entry here is based on, and footnoted to, at least one primary or secondary source, public or private, but all of it is subject to revision as new knowledge emerges. (The few unsourced exceptions are mostly collateral relatives of Patrick or Teresa where what we know comes from in-family knowledge, and we're gradually checking those against independent sources.) It's inevitable that some things presented here will turn out to be wrong. All genealogy is a work in progress.

Click here for notes on a few of our sources; here for the Teresa Nielsen Hayden Medieval Ancestry Lists Page; and here for several thousand too many words about genealogical trivia.