* _As Time Goes By_ (1982)
* _I'm Not Here_ (1983)
* _The Anatomy of Change_ (1990)
* _The Time Ship_ (1993)
* _The Unborn Yesterday_ (1995)
* _The Other Yesterday_ (1997)
* _The Return of Yesterday_ (1999)
* _The Yesterday Ring_ (2001)
* _The Shadow of Yesterday_ (2003)
* _The Echo of Yesterday_ (2005)
* _The Yesterday Secret_ (2007)
* _The Tomorrow Key_ (2010)
* _The Time Locker_ (2012)
* _The Yesterday Clock_ (2014)
* _The Time Puzzle_ (2016)
* _The Yesterday Mirror_ (2018)
Non-fiction:
* _How to Write Science Fiction_ (1982)
* _The Science Fiction Handbook_ (1985)
* _The Fantasy Handbook_ (1990)
* _The Horror Handbook_ (1994)
* _The Time Travel Handbook_ (1996)
* _The Alternate History Handbook_ (1998)
* _The Paranormal Handbook_ (2000)
* _The Apocalypse Handbook_ (2002)
* _The Future Handbook_ (2006)
* _The Science of Science Fiction_ (2008)
* _The Philosophy of Science Fiction_ (2011)
* _The Psychology of Science Fiction_ (2013)
* _The Sociology of Science Fiction_ (2015)
* _The History of Science Fiction_ (2017)