Check out the Internet, TV and movie screens, and it seems like everyone is wallowing in the past. Viewers 18 to 40, in particular, are obsessed with the Day-Glo, super-fun time that represents their youthful innocence, when endless viewings of “Clueless” and “Full House” were the centerpiece of many a sleepover. Fueled by social media, this interest in the pop-culture trappings of the recent past, particularly the ’90s, has become a fertile area for TV programmers, who are unleashing a flood of shows over the next year to capitalize on the ever-growing appetite for all things retro. Aiding in programmers’ quest to decide what should be revived, rerun or re-exploited: a veritable focus group of Internet obsessives steeped in, and celebrating, the past couple of decades.

That has translated to upcoming TV versions of ’80s and ’90s small- and bigscreen favorites including “Full House,” “Coach,” “Twin Peaks,” “Powerpuff Girls,” “The X-Files,” “Rush Hour,” “Duck Tales” and “Uncle Buck.” Movie reboots of “Jumanji” and “Jem and the Holograms” are also generating social-media excitement.

To understand the extent of the thirst for content that comes with a ready-made seal of approval from binge-prone fans, one need look no further than Hulu’s $160 million deal for off-net rights to all 180 episodes of 1990s NBC juggernaut “Seinfeld,” aimed at driving Hulu Plus subscriptions. It would be sheer conjecture to suggest how much revenue the current crop of redos can generate — and in the case of Netflix, which doesn’t share viewership data, it’s even harder to measure the impact of programming like “Full House” reboot “Fuller House.” But what’s changed from earlier cycles of reruns is how willing fans are to help promote these properties on social media, which can produce a nucleus of committed viewers who can turn modest performers into hits.

How many classic TV characters can you spot? Get the answer at the end of the article. Illustration by Kristian Hammerstad for Variety

The epicenter of this obsession with the stuff of preteen afternoons is, unaccountably, “Full House.” The family sitcom ran eight seasons on ABC, from 1987 to 1995, and although it rose into Nielsen’s top 10 twice, few in the industry would have predicted such continued interest in the show.

Yet on Aug. 22, Lifetime airs made-for-TV movie “The Unauthorized Full House Story,” and Netflix’s “Fuller House” reboot will premiere some time in 2016, with most of the principal cast members having signed back on. (A “Full House” musical parody touring show starring Perez Hilton also kicks off this month.)

“There have always been reruns and classic TV shows, but it seems like we’re in a new era of viewers who are fanatic about nostalgia for their favorite shows and characters,” says Keith Dawkins, TeenNick senior VP.

Andy Borowitz, who wrote for “Square Pegs” and “The Facts of Life” before going on to co-create one of the most oft-cited fan-favorites, “The Fresh Prince of Bel-Air,” says part of the appeal is the sense “that the past was awesome, and the present sucks.”Nick at Nite has kept “Full House” in circulation throughout the 2000s, taking off-net rights following TBS and ABC Family. Dawkins says part of the show’s appeal is that it crosses generations, becoming a rare program that kids can grow up watching with their parents.

Lifetime, which previously ran an “Unauthorized Saved by the Bell” movie, was only too eager to again tap into viewer loyalty. “We picked ‘Full House’ because it was so beloved,” says Lifetime senior VP of original movies Tanya Lopez. “The (cast) likes each other, and they’re still together.” (The movie was in development before Netflix greenlit “Fuller House.”)

Lifetime continues its head-first dive into nostalgia later this fall with “The Unauthorized Beverly Hills 90210” and, after that, its inevitable companion piece, “The Unauthorized Melrose Place.”

A “Back to the Future” documentary is also among several documentaries in the works that aim to examine every last morsel of ’80s and ’90s entertainment.

Netflix, too, is doubling down on the trend. On July 31, it premiered “Wet Hot American Summer: First Day of Camp,” a prequel to the 2001 film that was itself a retro celebration of life at a summer camp, set in 1981.

Much of the buzz around these reboots and spinoffs is fueled by the constant stream of shareable content on pop-culture websites.

One of the most popular among these is Buzzfeed’s Rewind section, which celebrates all things nostalgic. “Nostalgia hits this part of your brain and releases some kind of chemical that feels really good,” says Buzzfeed deputy editorial director Matt Stopera. “That ‘nostalgia chemical’ makes you want to share things with friends or people around you. Some of the best, easiest conversations with people are about old things.”

People in their 20s love to think they’re “old,” a sentiment that sites like Buzzfeed, the Chive and Popsugar mine frequently with headlines like “40 Things That Make You Feel Old,” based largely on TV, movie, music and videogame references.

Conventional wisdom was that it took four decades to recycle cultural movements. In a 2012 New Yorker article, “The 40 Year Itch,” Adam Gopnik explained that viewers were fascinated by the world of “Mad Men” because it took approximately that long for eras to become cool again: For example, ’70s films “The Sting” and “Paper Moon” celebrated the 1930s.But the cycle has sped up, and now the younger end of the nostalgia generation is already pining for the aughts. “We’ve seen a pretty big shift even in the past few years from late-’90s dominating nostalgia to more of the 2000-2004 area,” Stopera says. “Disney Channel shows from the early 2000s are having a renaissance.”

Witness the $5 million-plus raised on Kickstarter to produce a “Veronica Mars” movie spinoff. The 2000s-era UPN/CW series barely qualifies as nostalgic, but the enthusiastic response to the project shows that in some cases viewers are even willing to pull out their own wallets to fulfill the hunger for added content featuring departed favorites. “Veronica,” released simultaneously on VOD and in theaters, took in $3.5 million theatrically, with its legion of enthusiastic home viewers more than helping to recoup the remainder of its modest cost.

Stars of every era can now be found on Twitter, building direct bridges to fans. When John Stamos recently emerged from rehab to start filming “Fuller House,” he reconnected with the tweet, “What’s everyone listening to right now?” — and received hundreds of suggestions.

Paradoxically, the embrace of nostalgia on the Internet has led to a burgeoning interest in real-time events. From the live reads that the “Wet Hot American Summer” cast did to keep interest high for years, to the Goonies Day celebrations in Astoria, Ore., where that 1985 movie was filmed, reunions and festivals are growing in popularity. In the past decade, outdoor summer movie screenings, publicized largely by social media, have mushroomed into dozens of al fresco events in cities like New York, Los Angeles and Seattle — seemingly all of them showing “Clueless” and “Ghostbusters” once a season.

Fans hunger to see their favorite stars together again, whether in person or on TV. “There is nothing better than a television cast reunion,” Stopera proclaims. That was certainly the case when the “Gilmore Girls” reunited in June at Austin’s ATX festival, causing a Twitter tornado of excitement that was felt far beyond Texas. When the show launched last year on Netflix, its renewed popularity spawned podcasts, a book and live events. Likewise, the YouTube video of the “Saved by the Bell” cast’s reunion on “The Tonight Show With Jimmy Fallon” has racked up a startling 31 million views.

Jonathan Gray, professor of media and cultural studies at the U. of Wisconsin, Madison, says social media, which can reveal the extent of love for a show, is a better barometer than Nielsen, which just measures how many people watch.

His students are rabid viewers of “Friends” and “Fresh Prince of Bel-Air” and even throw “Golden Girls” viewing parties. “They want media that takes them to warm spaces,” he says.

But Gray cautions that reduced expectations frequently must be a part of the equation for those fashioning a reboot: The days of “The X-Files,” for instance, averaging almost 20 million viewers, as it did at the height of its run on Fox in 1997-98, are, for the most part, also the stuff of nostalgia. In today’s fractured media climate, a modest success may be the most a network can hope for. “What I learned from ‘Buffy’ is that when you bring something back from the dead, it’s always different,” Gray says.

But ratings or box office numbers aren’t always the only goal. “The Unauthorized Saved by the Bell Story” drew just 1.6 million viewers on Lifetime. But, Lopez notes, in the quarter in which the special aired, the older-skewing network registered one of its youngest quarters ever, with new viewers bringing down the median age from 47 to 35.

Vintage programming is an important part of Nickelodeon’s mix: TeenNick targets younger viewers with more recently departed series like “Drake and Josh” and “Zoey 101,” while older viewers can catch some top shows of the retro canon on Nick at Nite: “Friends,” “Fresh Prince of Bel-Air” and “Full House.”

The idea for Nickelodeon’s ’90s block was sparked by an intern who, in 2011, called the net’s attention to a Facebook group called “I Want My ’90s Nickelodeon Back.”

The kids who grew up with “Rugrats” and “Doug” are now deep into a career, and such shows are their comfort food, Dawkins says.

Networks in the business of nostalgia have devised strategies that maximize the use of social media. Nick is serving up related content on platforms like Snapchat, getting input from followers, and using fan-based minutiae to populate the online environment. Lifetime sends out a barrage of clips and photos that fans can share for programming like the “Flowers in the Attic” movies, based on the popular ’80s book series.

“Fresh Prince of Bel-Air” is another 20-year-old property that remains wildly popular on the Internet.

“No one could have known this at the time, but the many running gags on ‘Fresh Prince’ make it a great fit for the social-media age,” says Borowitz. “Jazzy Jeff being thrown out of the house … Carlton dancing — they’re ready-made GIFs.”

A new series “in the vein” of “Fresh Prince” was recently announced to be in a very early stage at Will Smith’s Overbrook production company. It’s been observed that despite their popularity, African-American sitcoms aren’t a major part of the reboot craze — yet. But, says Borowitz, “I think there’s massive nostalgia out there for black shows. If you go on Twitter, you’ll see that there are a lot of people who love ‘Martin,’ for example. The nostalgia is there and it’s huge, but TV executives haven’t really picked up on it yet.”

It’s too soon to say if the current surge of retro-mania is stronger than usual or just a continuation of a speeded-up cycle.

“When I was growing up in the ’70s,” Borowitz says, “the biggest hit was ‘Happy Days,’ set in the ’50s. By the 2000s, people had moved on to ‘That ’70s Show.’ ” The future of nostalgia can’t be far off, he adds: “In 2030, there will be a hit show set in the 2010s, poking fun at our incredibly primitive iPhones.”

Pictured in the illustration above, from left to right: Top row: “Uncle Buck,” “Doug” and his dog, the “Full House” gang, “The Powerpuff Girls,” “Clueless.” Second row: “Jem and the Holograms,” Mulder and Scully from “The X-Files.” Third row: Brenda and Brandon from “Beverly Hills, 90210,” the Log Lady and Agent Dale Cooper from “Twin Peaks,” Data from “Goonies,” “Saved by the Bell,” “Bill & Ted’s Excellent Adventure.” Bottom row: “Ducktales,” “Goonies,” “Buffy the Vampire Slayer,” “My So-Called Life,” “Fresh Prince of Bel-Air.”