Very similar to mixtapes and arguably their 2010s equivalent, a fanmix is a playlist of songs or music videos, created by a fan of a book, film, or television show, with the intent to invoke the atmosphere or attitudes of the characters and events of the narrative.

Fanmixes may be aggregated on a website such as YouTube or 8tracks, or they may be posted as nothing more than a text list of artists and song titles in the intended sequence for the mix, usually with an accompanying description and cover image for the fanmix, as though it is the playbill for an album. The latter format is especially popular on the blogging website tumblr.

A fanmix can focus on any aspect of a work of fiction. It might be oriented around a single character's history and development; it might be designed to evoke the emotions of a relationship between two characters. It might be relevant to a specific event or conflict in the story. A fanmix can also be created for ordinary life experiences, aesthetics, and things outside of media, such as the emotions related to a breakup or death in the family, or a cross-country road trip with one's friends.

There are fanmix memes and templates, such as "fanmix yourself" templates intended to allow somebody to depict their personality through the music playlist they share with other bloggers. Each item on the template sets a parameter for the fanmixer: one item might be "a song which makes you feel like dancing;" another might be "a song for kicking zombie ass during the zed apocalypse."

It is widely considered by fanmixers that fanmixes are a legitimate form of transformative art, just like fan art and fanfiction, or like a collage made with music instead of images and textures. Fanmixes usually feature between 11 and 25 songs. The fewer songs are used in a fanmix, generally the longer those songs tend to be; a typical fanmix lasts approximately one hour. It is also generally considered good form for any fanmix to feature two songs by the same artist, near the beginning and end of the mix, to serve as bookends and places for the music to loop nicely if the listener sets the mix on repeat. The band Bastille is an especially popular group to provide these bookend songs; many fanmixers regard their song Pompeii to be evocative of many significant emotions and therefore suitable to nearly any fanmix. In this way, the inclusion of Pompeii in a fanmix has become memetic to the point of humour for the fanmixing community.

The defining feature that sets a fanmix apart from any other playlist is its narrative structure. Instrumental music is used for a certain atmosphere; music with lyrics is used because the lyrics describe important elements of the story or emotions represented by the mix. Ideally the narrative 'arc' will have a clear sense of exposition and steady escalation from the beginning toward a climactic song, followed by a denouement of increasingly calmer and less intense music until the end of the mix. The first and final songs of the mix should have very similar atmospheres, for the sake of good looping.

Here I have provided an example of a 36 minute fanmix, focusing on pyrrhic victories and melancholy triumphs found in the Doctor Who television series and several other science fiction television shows and anime.

1. The Doctor's Theme (Series 1 & 2) - Murray Gold, Doctor Who Soundtrack

2. Innocent Days - Hitomi, Code Geass Soundtrack

3. Lilium - Kumiko Noma, Elfen Lied Soundtrack

4. Vale Decem - Murray Gold, Doctor Who Soundtrack

5. The Heart Asks Pleasure First - Michael Nyman, The Piano Soundtrack

6. Mosane - E. S. Posthumus, Cartographer

7. Decretum - Yuki Kajiura, Puella Magi Madoka Magica Soundtrack

8. Mirror, Mirror - Jeff Williams feat. Casey Lee Williams, RWBY Soundtrack

9. Sanctuary - Darling Violetta

10. Doomsday - Murray Gold, Doctor Who Soundtrack

11. Kara Remembers - Bear McCreary, Battlestar Galactica Soundtrack

Tracks 1 and 10 both carry the same vocal line, which allows cohesive bookends. The arc of the music begins wistful, growing increasingly tragic through track 4, before becoming very turbulent and energetic from tracks 5 to 7. Track 8 returns to a wistful and melancholy vocal music theme before revisiting the turbulence of the last several tracks and carrying it into tracks 9 and 10. Track 10 brings things to a slower but still very tense state, and track 11 wraps things up by starting tentatively and ending triumphant and serene. If the fanmix is looped, then the transition from 11 back to 1 is very nearly seamless.

Each song has some quality which revisits the one previous at least briefly: atmosphere, instrumentation, genre, language, etc. create a thread of pulsing continuity throughout the fanmix, and this continuity has many small crests and troughs of intensity and tempo, like a wave, all approaching the climactic intensity that the end of track 8 and all of track 9 carry. None of the songs is a sudden shock to the listener's system by having so starkly different a sound that it seems especially out of place relative to its neighbours in the list.

This is hardly a fanmix nonpareil, but it demonstrates all the fundamental principles involved in fanmixing.