- "This is what I'll say, and for whatever it's worth I do swear that this is not just promo nonsense. It's by far, the strongest of the stories. It's the movie that the series requires and deserves and it's the rightful third chapter; or third act, I should say. I don't think anybody will be disappointed."
- ―Jay Baruchel for JoBlo Movie Podcast 
How to Train Your Dragon 3, now officially titled How to Train Your Dragon: The Hidden World, is an upcoming animated movie produced by DreamWorks Animation and the sequel to How to Train Your Dragon 2. It is the third and final installment in the movie franchise and is scheduled to be released on March 1, 2019.
The film's existence was first confirmed in December of 2010 by DreamWorks CEO Jeffrey Katzenberg who stated that the How to Train Your Dragon series is an "at least three" chapter story, a statement further backed up by Dean DeBlois's comments about the second film being intentionally written as the second part of a trilogy.
"As Hiccup fulfills his dream of creating a peaceful dragon utopia, Toothless’s discovery of an untamed, elusive mate draws the Night Fury away. When danger mounts at home and Hiccup’s reign as village chief is tested, both dragon and rider must make impossible decisions to save their kind."
"From DreamWorks Animation comes the highly anticipated culmination of one of the most popular animated franchises in film history, HOW TO TRAIN YOUR DRAGON: THE HIDDEN WORLD. What began as an unlikely friendship between an adolescent Viking and a fearsome Night Fury dragon has become an epic trilogy spanning their lives. In this next chapter, Hiccup and Toothless will finally discover their true destinies: the village chief as ruler of Berk alongside Astrid, and the dragon as leader of his own kind. As both ascend, the darkest threat they’ve yet faced—as well as the appearance of a female Night Fury—will test the bonds of their relationship like never before." 
After Katzenberg's initial confirmation of How To Train Your Dragon 3's existence, 20th Century Fox and DreamWorks announced in September 2012 an initial release date of June 18, 2016. Just over two years later, the release date was pushed back until 2017, with DeBlois explaining that the animation, writing, and storyboarding process takes a minimum of three years for each movie. 2014 also revealed that DeBlois had managed to talk to Katzenberg and talk him out of a fourth film, though he is open to the possibility of spin-offs.
In January 2015, following massive corporate restructuring and a change of plan to release two films a year instead of three, DreamWorks announced the current release date for How to Train Your Dragon 3 was confirmed to be June 29th, 2018. In June 2016, the release date moved up to May 18, 2018, taking The Lego Movie 2's release date, while The Lego Movie 2 is delayed until 2019. In December 2016, the film's release date was pushed back to March 1, 2019.
The film is being produced by Bonnie Arnold, directed by DeBlois and executive produced by both Chris Sanders and DeBlois. Jay Baruchel, Gerard Butler, Craig Ferguson, America Ferrera, Jonah Hill, Christopher Mintz-Plasse, T.J. Miller and Kristen Wiig have all be confirmed to be returning for How to Train Your Dragon 3. Cate Blanchett, Kit Harington and Djimon Hounsou will also reprise their roles from the second film. John Powell will also return as the film's composer.
Much of the film's plot is still unknown, although small glimpses of its content have been revealed in interviews with DeBlois and the film's creators.
In 2014, both Cressida Cowell, the author of the original How to Train Your Dragon books, and DeBlois confirmed that, although the books and films have followed very different stories, they will both share the same ending of explaining why "dragons are no more".
DeBlois also noted, in an interview with Collider in October 2014, that the story will have more emphasis on Toothless as he wants to continue showing an insight into their perspective of the dragon world. In the same interview, DeBlois also revealed that Drago Bludvist's role was originally going to be the main antagonistic force in How to Train Your Dragon 3 before it was shifted to the second film and that he will become a much more complex villain for the third installment.
In February 2015, during another interview with Collider at the VES Awards, DeBlois shared more details of the plot. He explained that the third film acts as the "culmination of Hiccup’s coming of age". After the events of the second film where Hiccup and Toothless have become the chief of Berk and Alpha dragon respectively, the story will focus on how both characters will be trying to do what’s right for their kind, leading to an eventual outcome where Hiccup is able to stand on his own. The dragons' disappearance was also confirmed to be tied into this conclusion. DeBlois also confirmed that he was currently on Page 60 of writing the screenplay for the film. He also said the movie was going to have a bittersweet ending.
In April 2016, NBCUniversal buys DreamWorks Animation for $3.8 Billion for further future animation feature films. Universal Pictures will take over the distribution for future DreamWorks Animation films, including How to Train Your Dragon 3.
In June 2016, the release date moved from June 29, 2018 to May 18, 2018.
In December 2016, the release date was delayed for one year and the new release will be released on March 1, 2019.
On October 5, 2017 in a keynote speech for Animation Dingle, Dean at one point talked about how he had to rewrite the script late last year and mentioned that after he had rewritten the script using the view of a film goer, that Steven Spielberg's response to having read the rewritten script was, "Insane Congratulations. I cannot believe what I just read and I had a problem reading the last part of it through my tears. It's a complete unqualified classic and better than the original. I've never witnessed this kind of transformation from the last two drafts I read to this one. I only wish I had points." 
The film is promising to be visually stunning, the likes of which viewers have never seen before. In an interview, Kate Swanborg, Senior Vice President of Tech and Strategic Alliance for DreamWorks Animation, said they're creating a "vast world"-
- "Our next film is How To Train Your Dragon 3. So here we are at what I believe is maybe the culmination of his set of stories around the dragons and around Toothless and Hiccup and we are designing and developing a brand new world within this film that we’ve never seen before in the other two films."
“It is vast. Spacially it’s supposed to be just huge – so many football fields I can’t even tell you. There’s water and light and space and it’s stunning and crazy and there’s gonna be just tonnes of dragons in it. Figuring out how to put that on screen right now is one of the biggest challenges and most inspirational things we are doing at the studio. It is going to be jaw-dropping!''"
- ―Kate Swanborg for Verdict UK, November 6, 2017
The number of digital workstations is said to have almost doubled for the film, giving the animators ability to do things they've never been able to before, and in record speed. Dave Valvoord, Visual Effects Supervisor of DreamWorks Animation, said in an interview that compared to what they're working on for the third movie makes How to Train Your Dragon 2 look dated.
- "Because we’re calculating light correctly, it’s completely changing the richness of the films. In fact, if you watch clips from How to Train Your Dragon 2, they look very dated. What we’re doing right now just doesn’t compare. It’s really exciting."
- ―Dave Valvoord for ECP, November 9, 2017
On November 14, 2017, Deadline announced that F. Murray Abraham will be voicing a new villain, introduced as Grimmel. And rather than a Scottish accent, he'll don a deep-baritone voice in the classic villain sense. 
In an interview with Screen Rant in early January, 2018, Gerard Butler suggested his voice work on the film was now finished.
On April 17, 2018, DreamWorks posted to each of their social media accounts that the movie's official title will be How to Train Your Dragon: The Hidden World.
Also on April 17th, a spokesperson for the Annecy International Animation Film Festival announced that attendees will get a special sneak peek at the film during its 2018 activities running June 11-16. Dean DeBlois and the HTTYD movies have had special links to the festival throughout the years, giving it the benefit of such a reveal.
At Universal Pictures' presentation at CinemaCon 2018, "unfinished and unseen footage" was seen, revealing that the additional Night Fury will be white. Hiccup and Toothless are shown exploring a "hidden dragon world". Hiccup's age is estimated to be "20s".  
Also at CinemaCon 2018, it was explained that a hunter is out to kill Toothless and the female "Light Fury". It is uncertain if this hunter is Grimmel or Drago. 
- Hiccup Horrendous Haddock III (Jay Baruchel) - The newly crowned Viking chief of Berk and the one who initially trained the dragons. His dragon and best friend is Toothless, a Night Fury who became the Alpha of the dragons after the events of the second film.
- Valka (Cate Blanchett) - A former dragon rescuer and Hiccup's mother, now living on Berk after 20 years of isolation. Her dragon is Cloudjumper, a Stormcutter.
- Astrid Hofferson (America Ferrera) - A strong, independent woman and excellent fighter. She is also Hiccup's girlfriend, fellow Dragon Rider and future wife. Her dragon is Stormfly, a Deadly Nadder.
- Gobber the Belch (Craig Ferguson) - A seasoned Viking, blacksmith, and dragon dentist. His dragon is Grump, a Hotburple.
- Fishlegs Ingerman (Christopher Mintz-Plasse) - One of the Dragon Riders and a bookworm on the many traits and characteristics of most dragon species. His dragon is Meatlug, a Gronckle.
- Snotlout Jorgenson (Jonah Hill) - One of the Dragon Riders whose pride and arrogence often get the better of him. His dragon is Hookfang, a Monstrous Nightmare.
- Tuffnut Thorston (T.J. Miller) - A Dragon Rider, and one of the quarrelsome fraternal twins who share a green Hideous Zippleback. The head he rides is called Belch.
- Ruffnut Thorston (Kristen Wiig) - A Dragon Rider, and one of the quarrelsome fraternal twins who share a two-headed Hideous Zippleback. The head she rides is named Barf.
- Eret, Son of Eret (Kit Harington) - An ex-trapper who used to work for Drago but has now joined the Dragon Riders. His dragon is Skullcrusher, a Rumblehorn, who was passed over to him after Stoick died.
- Drago Bludvist (Djimon Hounsou) - A ruthless dragon hunter and madman who attempted to destroy Berk in his quest to take control of all dragons but was defeated by Toothless and Hiccup and presumed to be dead. The dragon under his control is a Bewilderbeast, one of the Alpha species who was beaten back by Toothless.
- Stoick the Vast (Gerard Butler) - The former Viking chief of Berk, Hiccup's late father and Valka's late husband. He was killed during the events of How to Train Your Dragon 2 and his exact role in the third film is unknown, although it has been hinted that his character will appear in flashbacks.
- Grimmel the Grisly (F. Murray Abraham) - A new villain, possibly an associate of sorts of Drago Bludvist.
- Unknown child (AJ Kane)
- Unknown (Taron Egerton) (awaiting confirmation) -
- New Characters will be revealed.
- On September 29, 2017, Simon Otto tweeted that the first three scenes of the movie had been finalized, and posted a picture of some paperwork with the title of the scene cleverly obscured by a pencil. 
- On April 1, 2017, Rotoscopers posted an article saying that the 3rd movie was being split into two movies; the second of which was due out in 2020. However this was an April Fools prank, as stated behind the "Original Source" link at the bottom of the article. It fooled millions, however, and even IMDb launched a page for "How to Train Your Dragon 3, Part 2" until informed fans had it taken down.
- On April 1, 2016, Rotoscopers posted an article saying that the 3rd movie was originally gonna have a PG-13 Rating. However this was an April Fool's prank, as stated behind the "Original Source" link at the bottom of the article.
- On April 17, 2018 the title How to Train Your Dragon: The Hidden World was confirmed.
- The film's theatrical showing will be preceded by an original DreamWorks Short, though the Short assigned to the movie is yet to be determined. 
- Due to the recent sale to NBC Universal, DreamWorks Animation is taking a year and a half hiatus though 2018 to reorganize. Their first film once they're back in commission will be How to Train Your Dragon 3.
- Jay Baruchel and America Ferrera have been confirmed as the lead voice actors in How to Train Your Dragon: The Hidden World. 
- Official Movie Website
- How to Train Your Dragon: The Hidden World on Wikipedia
- How to Train Your Dragon: The Hidden World on Rotten Tomatoes
- How to Train Your Dragon: The Hidden World on Metacritic