Wilf: God bless the cactuses! The Doctor: That's cactI. Alien: And that's racist!

[David Tennant's] Doctor has such humanity, he seems to understand us and he's very warm, so he's a comforting Doctor to be with, and he enables us to be slightly scarier than we had been.

I dread the day I leave [Doctor Who], because then I'll have to go back to writing bedrooms and offices and pubs. And maybe a field, if I'm lucky.

I would rather be confused for 10 minutes than bored for 5 seconds.

Harriet Jones: Did you notice when they fart, if you'll pardon the word, it doesn't just smell like a fart, if you'll pardon the word, it's something else. What is it? It's more like, um... Rose Tyler: Bad breath. Harriet Jones: That's it! The Doctor: Calcium decay. Now that Narrows it down!.. Calcium phosphate. Organic calcium. Living calcium. Creatures made out of living calcium. What else - what else? Hyphenated surnames. Yes! That narrows it down to one planet! Raxacoricofallapatorius! Mickey Smith: [sarcastically] Oh yeah, great! We can write 'em a letter.

Fun, that's the word I keep on using. That's the word I worry about when other writer's scripts get too dark. Optimistic. Fun. And to be optimistic and have fun there's got to be a darkness there. I think that's a very British attitude.

Doctor Who: You want weapons? We're in a library. Books are the best weapon in the world. This room's the greatest arsenal we could have. Arm yourself! (from Tooth and Claw in Season 2)