The K/S Star Trek fan fiction collection is a large collection of slash fiction portraying the relationship and interactions between Captain Kirk and Mr. Spock from The Original Series. These materials date to the early beginnings of the slash movement which grew out of Star Trek fandom and began around the time the show was cancelled in the late 1960s. These stories and art are primarily focused on characters from The Original Series but also include a small number of works from later Star Trek franchises, such as The Next Generation and Voyager. Sereis 2 includes slash pairings of other TOS characters and slash fanfiction from other franchises. Series 5 includes general fanzines and is not slash material.

The term "slash" comes from the use of the forward slash "/" used to denote the romantic pairings of characters. It is fanmade fiction and art that portrays canonical characters in non-canonical romantic or sexual relationships. Though the movement originated in Star Trek fandom, it has grown in popularity and a slash scene can be found alongside most major media franchises.

Throughout the collection there are a large number of items that were printed from various online and digital sources (forums, email, listservs, blogs, etc). These usually include a date of printing, and, on occasion a date of posting. Processing staff decided to mark these items as "undated" when only a printing or posting date are on the item and it was unclear what the date of original composition was. If the author of a story explicitly noted a date, then that was included.