James Corden is nervous.

The launch of his “Late Late Show” on CBS is just weeks away, and he’s questioning everything. The set. The logo. His wardrobe. Himself.

“There’s good nerves and there’s bad nerves,” he says. “It’s good nerves that spur you on, and bad nerves that debilitate you. If I can find the good nerves, I’ll be very grateful.”

The 36-year-old British comedian knows he’s facing an uphill battle to win over American audiences — make that even introduce himself to them. He may have nearly 5 million Twitter followers, but as he is quick to point out, “They’re all back in the U.K.”

He also has to win over celebrities — and more crucially, publicists, so that he can land key bookings for his couch. Despite his many talents, he’s never hosted a talkshow of this scale before, so reps are understandably skittish, wary of potential snark.

“I don’t know if I’m making a huge mistake,” Corden admits. “But I’d rather regret doing something than not doing something. I think we have a real shot at enjoying ourselves for a bit, which is ultimately all you ever really want, isn’t it?”

With all the changes in latenight TV during the past 16 months, there’s still plenty of room for a new voice in the wee hours. The challenge for Corden will be finding his.

(Photos by Zen Sekizawa for Variety.)

The “Late Late Show” team in recent weeks has ventured out into the Grove shopping center across the street from his studio at CBS’ Television City to work out some field pieces in preparation for the March 23 premiere. “James is new to L.A., so he has to meet his neighbors,” explains Nick Bernstein, the CBS latenight programming executive working with Corden’s team.

The pudgy star decides to play up his anonymity, and his naturally self-deprecating wit, by asking people, “What do you think of the new host, James Corden?” One woman says she doesn’t like the man, so he pushes her on her reasons: “Is it because he cut his long hair? Is it because he’s so thin?” “Yes, he looks like he’s wasting away,” she replies. Suddenly suspicious, she asks, “He’s not behind me, is he?” With a wink to the camera, Corden says, “No, we would never do that to you.”

Indeed, Corden is barreling onto the scene at a time of unprecedented upheaval in latenight. Jay Leno is gone. Jimmy Fallon is killing it. David Letterman and Jon Stewart are preparing for their final bows. Stephen Colbert has retired his faux-right-wing persona and is preparing to unveil an entirely new animal — himself — in the fall, while Jimmy Kimmel and Conan O’Brien redouble their efforts to woo new viewers. Larry Wilmore is still in his first inning. John Oliver has impressed by taking the form in a different, substantive direction on HBO. And Chelsea Handler promises to break the mold next year with her show for Netflix.

In the post-Johnny Carson era, the ups and downs of the latenight TV arena command outsized attention in pop culture, given the overall size of the audience in the day­part. According to Nielsen, the latenight shows airing in the 11 p.m.-2 a.m. frame are averaging a total of about 12.1 million viewers, led by “The Tonight Show With Jimmy Fallon,” with an average of 3.7 million viewers for the season to date. Time-shifted viewing is expanding that audience, but not at the same rate as it is growing viewership of primetime shows.

Success in latenight is a lucrative proposition for major networks. The shows are typically less expensive to produce than most primetime series — although Fallon’s “Tonight Show” is fortified with a hefty budget that is the envy of his rivals — and when a show clicks, its tenure is usually measured in decades, not season to season. According to Kantar Media, advertisers spent $1.9 billion in the 11 p.m.-1 a.m. daypart from January to September of last year, including $422 million on the four broadcast networks and $1.4 billion across dozens of cable nets.

Having a strong presence in the daypart is one of the key elements that feeds into a network brand — just ask Fox, which has struggled through its nearly 30-year existence to crack the code (and recover from the Joan Rivers and Chevy Chase debacles).

“There’s a unique connection between viewers and hosts in this time period,” says Rick Ludwin, the former NBC exec who steered the net’s latenight efforts for more than 20 years. Some of it has to do with the fact that viewers tend to watch as they’re winding down the day, and some of it comes from the Monday-Friday frequency, just as it is with network morning shows. Whatever the reason, the relationship is powerful and undeniable, says Ludwin, who helped Leno through his rocky first years on “The Tonight Show,” and did the same with O’Brien, Fallon and Seth Meyers, among others.

“It’s a more personal experience for people than they have even with their favorite primetime shows,” says Ludwin. “People connect with these hosts, and they almost become a member of the family. If someone announces they’re leaving, it becomes a personal matter.”

Building that relationship with viewers is the highest hurdle for Corden, who comes to the “Late Late Show” with virtually no name recognition over the vast expanse of America. When CBS announced in September that Corden would be taking over for Craig Ferguson at 12:35 a.m., you could hear the resounding “Who?”

“It’s madness, really. When I got the job, I’d never even been on an American talkshow,” Corden says. “It’s a bold choice. A really bold choice.”

Corden, who grew up in Buckinghamshire, began his career with small TV roles as well as stage work in “The History Boys,” then shot to fame as the co-creator, writer and star of the hit Brit sitcom “Gavin & Stacey.” It was his role in the play “One Man, Two Guvnors” that attracted international attention, especially once the show transferred to Broadway — and he won the Tony in 2012. Since then, he’s added a bit more Hollywood buzz with his star turn alongside Meryl Streep in “Into the Woods.”

CBS honchos Leslie Moonves and Nina Tassler had been casting a wide net for Ferguson’s replacement. Corden went in pitching a sitcom — and ultimately walked out with the latenight gig.

“I just could not stop laughing.” recalls Tassler. “His wit and sense of timing are impeccable; his charisma is undeniable.”

Tassler did a deeper dive into Corden’s background, and was won over by his gig hosting “A League of Their Own,” a British gameshow with rotating panelists.

When she told him she was considering him as Ferguson’s replacement, he was stunned, telling her, “I would swim across the Atlantic Ocean and walk across the United States barefoot on broken glass to get this job.”

(Photos by Zen Sekizawa for Variety.)

His first call — other than to his wife of 2½ years, Julia — was to his producing partner, Ben Winston. They’d met back when they were teenagers, and Winston was a PA on a show in which Corden had a small part. They’ve teamed up on countless projects since, including the Brit Awards and “James Corden’s World Cup Live.” But they knew they needed someone with latenight credentials, and so they lured Rob Crabbe away from the “Tonight Show” to join them as exec producer.

There’s no question Corden has talent to spare: He can sing. He can dance. And he’s got an infectious laugh that makes it impossible not to smile in his presence.

But there’s one thing he’s not, which has pretty much been a prerequisite for anyone aspiring to a latenight job: “I never will be a standup comedian,” he says. “It’s just not in my skill set.”

Which is why he, along with Winston and Crabbe, have been tinkering with every part of the latenight format; they want to play to his strengths.

“We’d be fools if we said that we’re going to just dynamite the entire idea of that format, but we also don’t want to marry ourselves to it,” Crabbe says.

As they consider every aspect of the show — “Is this the best use of our time? Is this the best use of me?” asks Corden, again and again — the word experiment comes up a lot.

Where the experimenting starts is with their choice of band leader: Reggie Watts (IFC’s “Comedy Bang! Bang!”), a musician and comedian known for his off-the-cuff improvisations, musical and otherwise (cue monster headaches for the clearance team). You’re never sure what you’re going to get with him — and that was the appeal for the “Late Late Show” team.

“He was on a list of one,” Corden says. “I just couldn’t get it out my head that this wasn’t the best idea for our show.”

Similarly, the structure of the program itself, which will air four nights a week (with reruns on Fridays), isn’t going to be traditional — starting with the monologue, or lack thereof.

Yes, Corden will greet the audience and say something funny — but producers aren’t planning a lineup of 20 jokes in classic latenight fashion.

“James is not going to be able to go out and do six minutes on Isis,” Crabbe says. “I just don’t think that’s going to be his style.”

The goal is to get to the guests faster. There’s a debate with CBS over how long the first act will be. If the producers get their way, the guests will be coming out in the initial part of the program — all at once. They’re modeling the show on Graham Norton’s U.K. series, in which all the stars come out at the same time and chat together on the couch.

But booking guests, the “Late Late” team admits, has been a challenge. “The hardest struggle is trying to convince people that this is a place where no one is ever going to be the butt of the joke,” Corden says. “All we want is our guests to shine, because if the guests shine, the show shines. If the show shines, then I shine.”

That said, thanks to booker Sheila Rogers, Corden did land an impressive lineup for his first week, including inaugural guest Tom Hanks, as well as Kerry Washington, Will Ferrell and Kevin Hart.

Getting top talent was the reason producers decided the show needed to be in L.A., which meant they all had to move their families here — including Watts, who pulled up stakes in Brooklyn. The team did a reality check concerning where they sat vs. the competition in New York and L.A.: They could be sixth rung in Gotham, behind Fallon, Letterman, Meyers, Colbert, etc. — or third on the left coast, behind Kimmel and Conan. It was an easy call: “We’ll take third,” says Corden.

What happens once everyone is settled comfortably on the “Late Late Show” couch is anyone’s guess. “We’re not just going to sit and talk to our guests,” Bernstein says. “But the great thing about James is he can do it all. If he wants to do some fun game with all of his guests, he can. And if he wants to sit and have an in-depth conversation with someone, he can do that, too.”

Corden points to a story that was in the news that day of a dog that walked 20 blocks to find its owner in the hospital.

“That’s the single greatest news story I have ever heard,” he says. “Maybe it’s our job as people go to sleep, to (feel) it could be better, but it could be a lot worse. Nothing would make me happier than just to have one person in one living room get me and get the show. It wouldn’t be enough for Les (Moonves), but it would be enough for me.”

Corden and Co. are inheriting a timeslot where Ferguson was consistently third to Meyers and “Nightline,” in both total viewers and the key 18-49 demo.

“The ratings are going to be what they are,” says Bernstein. “The most important things are getting people to sample the show, and continuing to make the shows better as they go on.”

Corden says CBS has been supportive, without setting any rating benchmarks to meet. “Of course, if I had my way, I would give anything to have the budget of ‘The Tonight Show,’ ” he says. “And it will be a constant frustration that we don’t.”

Even more critical to “Late Late’s” success will be timing. While the March 23 launch will attract a fair share of buzz, Corden and his team admit that the show won’t immediately find its feet. “It’s like eating a souffle after it’s been in the oven for 10 minutes,” he says. “These things are going to take time to rise.”

Their plan is to keep experimenting — there’s that word again — post-launch and beyond.

Says Winston, “If we come to a place in three months’ time, and we’re like, ‘act one looks like this, act two looks like that, act three looks like this,’ I think we would have wasted the opportunity of having real experimental fun at 12:30, which is what this show should be.”

Letterman’s send-off at the end of May will certainly bring another round of attention — followed by a long summer run without a lead-in. The “Late Late” team sees the show’s true launch as September, when it gets a crucial hand-off from Colbert at 11:35 p.m.

Despite the hyper-competitive climate, the producers don’t consider the other talkshow hosts as rivals: “Our competition is people choosing to fall asleep,” Corden jokes.

The fraternity of latenight hosts has reached out to Corden to offer support: A night out with Fallon. Dinner with Meyers. Texts from Colbert. A call from Leno.

The Scottish-born Ferguson phoned as well, to say, “There are only two people in the world who know what it’s like to come from a tiny island, move to Los Angeles and host a late-night talkshow,” recounts Corden, adding that Ferguson said it would be remiss of him not to offer his advice.

They all offered the same bit of wisdom: Be yourself. That’s terrifying, he admits, “because I’ve never been open.”

There’s one name missing from the list of well-wishers: Letterman.

Talking to Regis Philbin, who was filling in as a guest host on the “Late Late Show” during the Ferguson-Corden transition, Letterman last month criticized the Brit for not starting earlier. “Where’s the tubby kid who’s taking over the show?” he asked Philbin. “How bad does he want to do a show?” (Sources insist Letterman was joking.)

“I think he was just messing around,” Corden says. “I don’t fancy our chances of starting with a staff of four, including the host, on a set that doesn’t exist. I think he’s bright enough to never say it seriously, because to say it seriously would be absurd.”

Letterman may have been ribbing the new guy, but the issue of the workload in latenight is no laughing matter, industry vets say.

“The work ethic of the host is every bit as important as how funny they are,” Ludwin says. “If the show is not the first thing you think of in the morning and the last thing you think of at night, you’re not going to be successful. The audience has come to expect more than ever. You need to give up part of your personal life.”

Corden’s family has already made sacrifices, although his wife is hoping his new day job eventually will provide some stability compared with the itinerant life of an actor. Once the CBS deal was done, Julia gamely packed up the couple’s two young children — including a newborn — and relocated to L.A. Her perspective was that she’d finally get to see her husband on nights and weekends. As she put it, “That’s just not been our life for quite a while.”

Ever grateful, Corden is trying to take it all in stride, whatever the outcome.

“I just know that this is a moment in my life,” he says. “Good or bad, it is a moment. ‘Do you remember that time we moved to Los Angeles and I tried to host a latenight talkshow?’ ‘Oh yeah, that was ropy, but it was a fun ride.’ ”

Cynthia Littleton contributed to this report.