A series of alternate historic fantasy by Harry Turtledove.  A subseries of the larger Videssos series.

A sub-series of science fiction novels taking place in the Commonwealth Universe by Peter F Hamilton.

A series of science fiction novels and short story collections by Lois McMaster Bujold centering around Miles Vorkosigan and his parents Cordelia and Aral.  This is the series in original publication order.

A series of science fiction novels by Daniel Young.

A series by Brandon Sanderson set within the Cosmere.

A science-fiction and fantasy cross-over series by Christopher Stasheff set in the DDT-verse.

A series in the DDT-verse by Christopher Stasheff.

A series of books about zombies written by Isaac Marion.

A series of science fiction books written by Jack L Chalker.  These take place in the Well World universe.

A sub-series of the Mistborn series by Brandon Sanderson set within the Cosmere.  This series takes place about 300 years after the first trilogy.

An overarching series of all Well World book by Jack L Chalker.

This is a four book series which retells the Welsh Maginogion.

Robert Jordan's epic fantasy series that was finished by Brandon Sanderson after his death.

A series of books based on the Oz books by L Frank Baum.

A duology by R M Meluch.

The eighth the Dray Prescot series.

A series of science fiction / fantasy books by Andre Norton that is a part of the larger Witch World series.

A series of fantasy novels originally written in Poland.  The Polish series is entitled: Saga o wiedzminie.

A dualogy by Roger Zelazney also know as the Changeling Saga.

A series of fiction stories written by R J Palacio.

A collection of Poe's stories in five volumes.

A fantasy series written by Lois McMaster Bujold.

A science-fiction series by Philip Jose Farmer.

A supernatural fantasy series written by Russian author Sergei Lukyanenko.

A series of science fiction by Orson Scott Card.

A trilogy of books that tie i3n to the X-Men comic books by Marvel.

X-Wing Series from the Star Wars universe.

A series released by DAW of fantasy short stories edited by Lin Carter at first and then by Arthur W Saha later.

A series of novellas based on the children of Luke, Leia and others in the Star Wars universe.

A science fiction series by John Brunner

A science fiction series by Vernor Vinge