"Viva Forever" is a song by English girl group the Spice Girls from their second studio album, Spiceworld (1997). The song was co-written by the group with Matt Rowe and Richard Stannard, while production was handled by the latter two. It is a pop ballad with Spanish-style elements. The song's theme is about a summer romance during a holiday vacation, as the lyrics discuss recent experiences and memories. It was released as the album's fourth and final single on 10 July 1998 by Virgin Records.

The single's commercial release was delayed several times and was poorly promoted, being affected by Geri Halliwell's departure and the subsequent continuation of the Spiceworld Tour by the remaining members. The song was well received by most music critics, with some considering it their best work artistically in 1998. It was a commercial success, debuting atop the UK Singles Chart, becoming the group's seventh number-one single in the United Kingdom and staying at the position for two weeks. It has since been certified platinum by the British Phonographic Industry (BPI). The song was also successful on the music charts in the rest of Europe, as well as Canada and Oceania.

An accompanying music video, directed by Steve Box, features stop motion animation of the group as fairies, and it took five months to be completed. The video was commissioned months before Halliwell's departure and as such, she is featured in it and on the accompanying artwork.

In May 1997, the Spice Girls went on a promotional visit to the Cannes Film Festival in the south of France, where they announced their then-upcoming movie Spice World (1997). The group began shooting scenes for the movie in June. Meanwhile, Virgin Records started the first marketing meetings for the promotional campaign for their second album Spiceworld, which was set to be released in November 1997. No song had been written for the album at this point, so the Spice Girls had to do all the songwriting and recording at the same time as they were shooting the movie. Between takes and at the end of each filming day, the group usually went straight into a mobile recording studio set up in a Winnebago, which followed them between film sets. Their schedule was physically arduous with logistical difficulties, as Melanie Brown commented in her autobiography: "doing the two full-time jobs at the same time took its toll and within a couple on weeks, exhaustion set in".

For the album, the Spice Girls worked with the same songwriting teams and producers from their debut studio album, Spice (1996). But during the recording of the Spiceworld tracks, the group was so busy with the filming schedule that the quality of their musical contributions became more erratic and piecemeal. Andy Watkins, of the production duo Absolute, co-writers of "Who Do You Think You Are" (from the band's previous album) remembered: "We'd sit there literally all day long and quite often we wouldn't even get them at all." Eliot Kennedy, who co-wrote "Say You'll Be There" with the group, worked on a couple of backing tracks for Spiceworld, but decided not to get involved in the album after hearing from the other teams about the complications of the recording schedule.

"Viva Forever" was one of the last songs the group wrote for Spiceworld. It was written at the end of the summer of 1997, after the filming for the Spice World movie had finished. Originally entitled "Obrigado", which means "thank you" in Portuguese, it was later renamed. The song was written by the Spice Girls with the songwriting team Richard "Biff" Stannard and Matt Rowe. They later confirmed that the lyrics were mainly penned by Geri Halliwell. The inspiration for the song's theme came from the idea of a summer romance during a holiday vacation on the Costa Brava or Costa del Sol in the Spanish Mediterranean, and the people the group met during those holidays. Emma Bunton commented about the songwriting process:

When we sat down to write it, we were talking about holiday romances, so that's what came out in the studio. I don't think I've ever had a real holiday romance, but I've met people I'll never forget. You meet so many different people and have nice or weird or romantic experiences with them, and you never forget them, do you?

Musically, "Viva Forever" is a pop ballad with R&B influences, and Spanish-style elements. It is written in the key of E♭ minor, with a time signature set in common time, and moves at a slow tempo of 84 beats per minute. The song starts with an instrumental introduction that includes keyboards, an acoustic guitar played by John Themis, and a string section arranged by English composer Anne Dudley. The song is constructed in a verse-chorus form, with an instrumental interlude before the bridge and the third chorus. It uses the sequence of E♭m–B♭m–C♭–G♭ as a chord progression during the verses and the chorus. The song employs Spanish production, including the sounds of castanets and guitars, a flamenco rhythm, and Spanish lyrics–"hasta mañana", translated as "until tomorrow", and "viva" itself, meaning "long live" (i.e.: Viva forever means "live forever", also written in the chorus's lyrics), as the lyrics were mostly written by Geri Halliwell who has maternal Spanish blood and speaks broken Spanish. Tom Ewing from the e-zine Freaky Trigger described it as "wistful music", while Alexis Petridis of The Guardian said that the song has a "note of melancholy" around it.