The Sidewise Awards for Alternate History were conceived in late 1995 to honor the best English-language alternate history genre publications of the year. The first awards were announced in summer 1996 and honored works from 1995. The award takes its name from Murray Leinster's 1934 short story "Sidewise in Time", in which a strange storm causes portions of Earth to swap places with their analogs from other timelines.
To be considered, a work must have either first English-language publication or first American publication* in the calendar year prior to the year in which the award is to be presented. Thus, the awards announced in 2009 honored works published in 2008 and were called the "2008 Sidewise Awards".
Two awards are usually presented each year. The presentation is normally made at the World Science Fiction Convention if that event occurs within the United States.
The Short-Form Award is presented for the best work of less than 60,000 words. This includes short stories, novelettes and novellas, and poems. One winner was a three-issue comic book series.
The Long-Form Award is presented for the best work longer than 60,000 words. This category includes individual novels and longer works. If a book is part of a series, it must be able to stand on its own to be considered. If it is part of a serial novel — a series in which the storyline is continuous and no volume can stand on its own — the complete serial novel will be considered when the final volume is published.
In addition, at the discretion of the judges, a Special Achievement Award may be presented to honor a specific work published prior to the inception of the Sidewise Awards in 1995, for a significant body of work, or for other contribution to the alternate history genre. As of 2023, this award has been presented four times, in the first three instances for a work or works published before 1995. The fourth honored an effort made over a period of almost 20 years but not a specific work.
* In practice, the qualifying year for works first published outside the United States varies between the year of first publication and the year of first publication in the U.S., and depends on when the Sidewise judges are able to obtain copies the work. Thus, some alternate history works first published in the U.K., Canada, and Australia may not be considered until they later receive publication in the United States. This was especially true in the early years of the Sidewise Awards and explains why, for example, Stephen Fry's Making History was considered for the 1998 awards on the basis of its first U.S. edition, rather than for 1996 when it was first published in the U.K. More recently, Richard Beard's Acts of the Assassins was published in the U.K. in 2015, but was considered for a Sidewise Award for 2016 after it was republished in the United States (and re-titled, as The Apostle Killer).
Exemptions to the first-year-of-publication rule may also be granted when a work's first publication was extremely limited and/or obscure. For example, Howard Waldrop's "You Could Go Home Again" was considered for the 1995 awards when it appeared on a popular science fiction website because its original publication in 1993 in chapbook form had a very limited distribution.