The Falling Kingdoms Series:
* The Shadow Throne (2011)
* The Fire Star (2012)
* The Wings of War (2013)
* The Sky of Stone (2014)
* The Kingdom of Ash (2015)
The Children of the Moon Series:
* The Children of the Moon (2016)
* The Moonstone (2017)
* The Shadow Queen (2018)
Standalone Novels:
* The Diviners (2017) - a historical fantasy set in 1920s New York
* The Shadow of the Leopard (2004) - a historical fantasy set in Victorian India
* The Last Voyage of the Nightingale (2005) - a historical fantasy set in 18th-century England
* The Necromancer's Daughter (2007) - a historical fantasy set in 18th-century England
Other Works:
* A Matter of Magic (2002) - a collection of short stories
* The Ghost of a Rose (2008) - a novella
* The Spell of the Black Moon (2014) - a novella
Katharine S. Ayres has also written extensively for the "The New York Times" and has been featured in various publications like "The Washington Post" and "USA Today".
This list is not exhaustive, but it provides a good overview of Katharine S. Ayres's writing. You can find more information about her works on her website or on Goodreads.