- In casting the role of Arthur, the decision was between Bradley James (who took the part) and Ben Mansfield.
- On 21 June 2009, this series was broadcast on NBC in the U.S. It marked the first time a UK drama has aired on a major U.S. network since The New Avengers (UK) over 30 years ago.
- The following actors have all appeared in separate episodes of Doctor Who (UK): Colin Morgan, Richard Wilson (ii), Anthony Head, Angel Coulby, Eve Myles, Lindsay Duncan, Michelle Ryan, Joe Dempsie, Georgia Moffett, Sarah Parish, Pauline Collins, Alun Raglan, Rick English, Alex Price (V), Colin Salmon, Jem Wall, Sarah Counsell, Tom Hopper, Miranda Raison, Tom Ellis, Greg Bennett (XIII), Philip Davis 'Juilan Glover' and Liam Cunningham.
- The distributor FremantleMedia Enterprises sold series one to 52 broadcasters in more than 180 countries, and the sales of series two resulted in buyers in more than 165 countries.
- According to cast members, Bradley James is a vicious prankster, with Angel Coulby getting the most flack from him.
- The archivist Geoffrey of Monmouth (played by Michael Cronin), who appears in several episodes, has the same name as the medieval author of 'The History of the Kings of Britain', one of the most important sources of Arthurian legend.
- Production Process: A French stuntman broke one of his ribs while shooting a jousting scene, the balsa wood on the end of lance the other stuntman was using didn't shatter correctly.
- Emilia Fox was pregnant during the filming of Series 3.
- Katie McGrath uses her natural Irish accent in the series, while Irish actor Colin Morgan fakes an English accent. Katie almost didn't get her role because "Merlin" producers didn't want two actors speaking with an Irish accent in the series, and they were ready to reject her for a role if she couldn't sound English, that is if Colin couldn't nail the English accent first.
- Colin Morgan often has to stand indoors or in the shade when he's not shooting to avoid looking pale in one scene and tanned in the next.
- Rupert Young who plays Sir Leon was only suppose to appear in one episode however fans loved him so much that the writers decided to have him as a recurring character. In Season 4, he finally became a series regular.
- Each season has thirteen episodes.
- Two part episodes include: - S2, Episodes 5-6 Beauty and the Beast - S3, Episodes 1-2, The Tears of Uther Pendragon - S3, Episodes 12-13, The Coming of Arthur - S4. Episodes 1-2, The Darkest Hour - S4, Episodes 12-13, Sword in the Stone - S5, Episodes 1-2, Arthur's Bane - S5, Episodes 12-13, Diamond of the Day
- John Hurt (The Great Dragon), Mark Williams (The Goblin), Michael Jennings (Sidhe Elder), are the only individuals who do not appear in physical form on the show. Only their vocal talents are used.
- Camelot Knights included: Sir Owain, Sir Pellinore, Sir Bedivere, Sir Leon, Sir Lancelot, Sir Percival, Sir Gwaine, Sir Elyan, Sir Mordred.
- It takes about four hours for Colin Morgan to be transformed into Emrys with prosthetics.
- In the scene where the witch Mary Collins declares revenge on Uther, the actress, Eve Myles, gave such a performance that the French extras (who didn't understand a word she said), applauded spontaneously, and Anthony Head (Uther) demanded to reshoot his lines, saying "I'm not good enough!"
- In the original draft of the script; Arthur and Merlin's first initial fight intended the characters to be shirtless, this idea was later changed, because the production team thought it was too severe and strong for a playful first fight.
- First appearances of Uther, Gwen, Gaius, Prince Arthur, Morganga and Prince Arthur.
- First appearance of Nimueh.
- The first kiss on screen was in S1.4 where Angel Couulby (Gwen) kisses Colin Morgan (Merlin) in Gauis's chambers when he wakes up after being poisoned by the Mordius flower.
- First appearance of Lancelot.
- Colin Morgan (Merlin)'s first stunt was in Season 1.7. Magical character Aulfric uses a magical staff to throw Merlin into a brick wall in a guest bedroom in Camelot.
- Bradley James(Arthur)'s first on-screen kiss was in S1.7 where he kisses Holliday Grainger (Sophia) in her bed chambers after she possessed him with magic.
- The last appearance of Nimueh.
- The mystic runes around the jewel on top of Sigan's casket are actually Kartuli, the language used in the Republic of Georgia in Eastern Europe. There are three extra characters thrown in that are not actually in the Kartuli alphabet, so the runes don't spell any actual words.
- The first appearance of Sir Leon.
- Bradley James (Arthur) and Angel Coulby (Gwen)'s first on-screen kiss was in S2.2 in her home. He kissed her good-bye as the sunlight streamed through the house windows.
- In Norse mythology, Freya, or Freyja, was the goddess of love, beauty and fertility. She was also supposed to love Spring and flowers.
- Bradley James who plays Arthur did his own stunt fighting with broad sword, bo, and hand-to-hand combat in the fight scenes against Lady Vivian's father, King Odin.

