Both have been going for a decade, both have offered various surprises over the years and both festival and band have grown bigger and bigger as time has gone by.
It's fitting, then, that tomorrow sees the Glasgow fivesome play a special show at the Old Fruitmarket, performing new music while backed by visuals from various filmmakers that have been created just for the show.
The gig forms part of the GFF's music and film strand, which also includes documentaries like The Punk Singer and films like Spanish tale Living Is Easy With Eyes Closed.
Fallow's one-off Fruitmarket show is certainly more complex than the average gig.
"We were really lucky to get a friend of the band, Tom Harrison, who's a freelance filmmaker, onboard, because we felt that we needed someone who knew the film world to co-ordinate everything," says Fallow drummer Phil Hauge.
"We had a chat with him and threw ideas back and forth until we settled on an anniversary theme for the night, as the film festival is 10 and the band is approaching 10, so that's where that idea came from.
"We've sourced 10 short films, loosely using the word anniversary, and then we've been writing new music around it. We've met a couple of the filmmakers, if they live in Glasgow, to see what they think about what the music could do, and gone from there."
It's certainly provided the band with a new way of working, as they've been writing music around the short films, rather than from scratch. But the group - Phil, singer Louis Abbott, bassist Joe Rattray, keyboardist Kevin Brolly and flute and piano player Sarah Hayes - welcomed the challenge.
"What we watched on film would determine the character or atmosphere of the song," says Phil.
"There were a couple of films that we thought would suit a classic song, a more traditional pop tune, and then there were ones that were more abstract, and suited to music like that.
"It's been a bit of free reign for us musically, and we can bounce our own interpretation of these films off that."
Tomorrow's birthday bash celebrates the fact the members of Fallow have all been living in Glasgow for a decade, although it took a couple of years for the group to become the unit they are now.
Things have been rolling in the right direction ever since, with 2010's Boots Met My Face and 2012's Tree Bursts In Snow mixing dark lyrics with strong melodies.
Two years have passed since Snow was released though, and fans eager for new material will be able to hear "three or four" new songs tomorrow, as the band will also play a full set of old and new tracks after the film portion of the night is done.
"We've been trying to take a bit more time with this album," explains Phil, describing the work on the next record.
"A lot of the time in the past Louis would come up with a lyric or a tune on the guitar, and we'd then work from there, but this time we had no songs to start with, so we've been rehearsing them on our own.
"We're halfway through it - we're hoping to start recording it by the summer, and hopefully have it ready for early next year."
Taking a new writing approach has also meant some changes in the overall sound of the group, and Phil reckons the whole band is coming to the fore more.
"I think in certain respects it will sound a lot different to people," he explains.
"There's more of an overall band sense to them, the drums are busier and the arrangements aren't as limited as we've not had lyrics as a base, to work around. It's a bit louder, and folk will say there's quite a change."
Yet while the band have one eye on the future, their recent Film Festival collaboration has also helped them reflect on the past.
"Having this project, and the whole 10 years thing, has made us think of all the time we've spent in Glasgow," he says.
"I don't feel particularly old though, music keeps you young! It's been nice to look back, particularly at all those early gigs in wee Glasgow venues, lugging our gear out of taxis and up the street."
n Admiral Fallow, Old Fruitmarket, tomorrow, £15/£12, 8pm.