Primeval follows a secret government research team, which is tasked with investigating doorways through time and space called Anomalies which are opening and allowing deadly creatures from across Earth's distant past and future to cross into and run rampant in the present. While predicting and discovering more about the Anomalies, the team must also contain the creatures and send them back through to their time periods whenever possible.
The first series of Primeval focuses on the newly-founded research team's attempts to combat the Anomalies and learn about and predict them. It also initially focuses on team leader Nick Cutter's search for answers on how the Anomalies are linked to the disappearance of his wife Helen eight years ago, and then later on what Helen's agenda is and who's side she's on. It is ultimately discovered that Helen merely wants to know more about the Anomalies for herself and does not care about the damage they are causing. At the end of the series, after returning from a mission into the past, Cutter discovers that team government official Claudia Brown has been erased from the timeline while he was in the past.
In the second series of the show, as the team are now part of the Anomaly Research Centre, it focuses on Cutter's struggle to cope with losing Claudia Brown and with the arrival of the team's new PR guru Jenny Lewis, who seems to be Claudia's doppelganger in the new timeline. It also focuses on Helen Cutter's and Oliver Leek's mysterious plans for the Anomalies and the creatures, and on Stephen's relationship with Helen and Connor's with Caroline Steel; and how this affects Connor and Stephen's other relationships with their friends. Leek's and Helen's plans are ultimately stopped and Leek killed, but Stephen is killed in the process.
In the aftermath of Stephen Hart's death, the ARC team go through several challenges and up against enemies; including Christine Johnson's plans for the Anomalies and attempts to take over the ARC, and Helen's deadly mission to save the future by attempting to destroy the ARC, killing her husband and later, trying to stop humanity from evolving. Johnson and Helen are both ultimately killed, but Connor, Abby and new team leader Danny Quinn are left marooned in the past.
Series 4 focuses on how greatly the ARC has changed in Connor and Abby's absence and on the two's changing relationship; and on new team leader Matt Anderson's mysterious mission and his attempts to protect Victorian time traveller Emily Merchant from the murderous Ethan Dobrowski. Eventually, it is revealed that Matt is secretly from the future and has been sent back to stop the ARC from using the Anomalies to destroy the planet, and that a massive phenomenon with the Anomalies will soon occur.
Shortly after the events of Series 4, Philip Burton fully recruits Connor into his New Dawn project with the Anomalies, while Matt and the newly-recruited Abby secretly work against them to stop New Dawn from destroying the future. The fifth series initially focuses on how Connor and Abby's opposing views and allegiances affects their relationship, and then later on the ARC team's efforts to stop Philip and New Dawn. New Dawn is ultimately destroyed, but Matt then encounters a battered double of himself telling him he must "go back".
Producer Tim Haines had the idea for Primeval around the same time he was making the award-winning Walking with Dinosaurs (1999).
Primeval was initially called "Cutter's Beastiary" and was a BBC project, however they weren't interested in the idea, they were at the time, in the process of bringing Doctor Who back and weren't interested in doing two sci fi shows. Tim was introduced to writer Adrian Hodges and together they wrote the initial three script and Tim's company Impossible Pictures took it to ITV who accepted it. Framestore was to provide the visual effects for the creatures as they had worked with Impossible Pictures on the Walking with... series, Chased by Dinosaurs, Sea Monsters and Prehistoric Park. 
Co-creator: Tim Haines said:
"Having introduced the animals to television and documentaries, I always thought, well, if you could bring [the creatures] into drama, make these a part of the story, make them perform a role, then there would be lots of potential for them. So I was very excited about the idea of trying to move this wonderful technology, this dramatic tool, into ordinary tv drama." 
"Its hard work. Ninety percent of the drama, despite having all these creatures in it, is about the convincing performance of the actors, the emotions that come across, the telling of the story. All these things have to happen on location" 
Co-creator: Adrian Hodges said:
"I knew if I could come up with a story that would match those special effects; we'd have something really unique. We didn't want spooky old churches or ghostly houses and things, we wanted something that felt really really modern. The idea we've had from the begining was that we wanted people to feel, having watched this programme, they could go into their kitchen and find a dinosaur in the kitchen. You know, they'd actually feel that close." 
Haines was keen to take a different approach to the Walking with... creatures, which were as scientifically accurate as possible. Primeval's creatures were, whist mostly based on real animals, aimed at being more character based. They needed something more cinematic. Extra spikes, brow ridges and horns were added of structures changed to make the creatures more scary. 
The first three episodes of Primeval were written by Hodges before any casting had been done.
Primeval initially ran for three series, with four episode novelisation books, four new story books, an interactive game, a line of 5.5" action figures and other toys being made.
Despite rumours near the end of Series 3, ITV denied that they would cancelled Primeval but were waiting for the show to finish airing before recommissioning another series.
On 15 June, 2009, after the broadcast of Series 3, ITV announced that they had cancelled Primeval and would not be making a forth series. A likely contributing factor to the cancellation was ITV's suffering severe financial troubles during 2009, reporting a £105 million half-year loss. As a result, some of its other popular shows including Heartbeat were axed.
On 29 September 2009, it was announced that a deal had been struck between ITV and fellow television channel Watch to revive the programme, and another 13 episodes of the show were to be filmed and produced in 2010 then aired as two separate series. In an effort to cut costs and use generous Irish Tax incentives for television production, filming moved to Ireland, starting on 22 March 2010. Framestore no longer supplied the visual effects with The Mill taking over. Series 4 and Series 5 were transmitted between January-February and May-June, 2011.
Series 6/the future of Primeval
Fans have hoped following the broadcast of Series 5 of the original Primeval show that it would be renewed for a sixth series. However, the producers claimed that it would not be produced if at all until 2013, and have expressed doubt that there will be a Series 6. With 2013 past, it seems unlikely that Primeval will get another series.
Tim Haines also stated there were not current plans to continue Primeval in other media other than television but he and Hodges would be happy to continue the show if a broadcaster came forward.
The unnamed film would be a spin-off movie of Primeval. The movie had been rumoured/planned for several years with talks of the film as late as 2012. The film would not be in the same canon as the TV show, most likely having different actors.
When broadcast/sold overseas, Primeval was renamed:
Primeval - Rückkehr der Urzeitmonster (Return of the primitive monsters) in Germany.
Nick Cutter et les Portes du Temps (Nick Cutter and the Doors of Time) for Series 1-3 and Les Portes du Temps (The Doors of Time) for Series 4-5 in France.
Pravēk Útočí (possibly meaning Prehistory Attack) in the Czech Republic.
The number of episodes in each of the five series of Primeval goes 6, 7, 10, 7 and 6.
In the Death in Paradise episode "A Dash of Sunshine", Primeval regulars James Murray and Hannah Spearritt appeared alongside Ben Miller. The episode also aired on the 12 Feburary 2013; six years and two days after the very first Primeval episode.