Where does your fascination with fairies come from? What were your sources of documentation for writing the trilogy of Tithe?

I've loved faeries for a long time. I grew up hearing stories from my mother and I have a vivid memory of finding the book Faeries, illustrated by Brian Froud and Alan Lee. There were snippits of folklore along with the images and it send me looking for more folklore and more stories of these capricious and dangerous beings. What I love most about faeries is that though they may look like us, they are no more like us than a summer storm. They have their own fierce, alien natures.

When I started Tithe, I started with a single image a girl with iron cuffs softly burning her wrists. From there, I realized I wanted to tell the story of the "tiend" or tithe that faeries pay, as referenced in the ballad of Tam Lin. Some of my favorite research books are W.Y. Evans-Wentz's Fairy faith in celtic countries, Dermot MacManus's The middle kingdom and almost anything by Katharine Briggs. I also found Yeat's writing about faeries to be incredibly inspiring as were my favorite urban fantasy writers: Terri Windling, Charles de Lint, and Emma Bull.

In White Cat, what came first, the history of Cassel and his family or the universe you created around them?

My idea for Cassel and his family came from reading a true crime book, Son of a grifter, about a boy who grew up with a grifter for a mother. Growing up with a warped sense of right and wrong -- one where everyone who wasn't in the family was a mark to be conned -- fascinated me. I knew I wanted to write about someone in those circumstances and I knew I wanted to retell an old French fairytale, "The White Cat," so when I put those things together, I knew I had to have a magic system that would work well in a book about crime and which would let me have the magic I needed for the fairytale retelling. From there I got to The Curse Workers magic system and the Curse Workers universe. 

In Spiderwick, the illustrations are as important as the text. How was the process to work in the series? Where the illustrations created from the text or vice versa?

Tony taught me an enormous amount about the role of illustrations and text. He would say, "if you described that part, then I'm going to illustrate the part you didn't describe" so that the illustrations were always adding to the story just like the text was. Most of the time the illustrations came after the story, but sometimes Tony would send me something (like the knocker character) and say, "can you write a scene for this guy?" Sometimes he would even have ideas for what might happen in the scene. So, it really was a collaborative process. 

One of your most famous series, Chronicles of Spiderwick, became a movie. How much influence did you have in the adaptation process? Are you happy with the result?

I am really, really happy with the film adaptation. I think the movie is a lot of fun and I think the characters seem like themselves. The film, to me, was true to the heart of the book series and I think that's the most important thing.  The producers and the director were really great about keeping Tony and I involved in the process. We got to see all the screenplays and to give our thoughts. We got to come out to the set and meet with the visual effects people. Obviously, we took take a backseat to the people actually making the movie, but they kept in regular contact with us and listened to us, so there really isn't any more I could have asked for. 

The Chronicles of Spiderwick and White cat are completely different stories, but they both have in common  the importance of the relationship between brothers. Is it a coincidence or something with which you like to experiment? In which ways do you think this relations help to enrich the story? 

I love complicated family dynamics our families are part of what makes us who we are, whether we like it or not. I think forcing the character to deal with their family gives us insight into them and enriches our understanding of their circumstances.

As an author you've tried a lot of different styles, all related to fantasy literature. You've written middlegrade and YA books. Have you thought about writing something for adults? What do you think of the fact that White Cat, in Spain, has been published in an adult collection? 

I thought about writing White cat as an adult book so it's interesting that it has wound up being published as one in several countries. I would like to write an adult book at some point, but so far I have been drawn to younger stories. There is something really interesting about characters young enough to be experiencing things for the first time and trying to figure out who they are and where they belong. The stakes are very high in teen books and in middle grade.

Urban fantasy, dystopians, vampires, angels ... Nowadays it seems that, if you don’t write something that matches with the fashion, your book is relegated to the background. Who are responsible of creating this fashions? Publishers, authors or readers? What do you think about this? 

At the end of the day, it's readers who create trends. Publishers can believe a book is going to be big and they can make sure that a book gets a lot of marketing and a beautiful cover, but unless it's embraced by readers, it's not going to be a phenomenon. Readers are the ones who press books into their friends hands and tell them, "you'll love this." Readers are the ones that spend hours online creating fansites, drawing fanart, and getting into conversations with other readers who loved the book as much as they did. Readers create trends; publishers follow them.

What is your usual working method? Do you start with a character, with a plot or with something different?

I always start with a character and sometimes with a premise. But I know I'm not ready to start until I have the right first line. Then I write a little, then plot a little, then write a little again. I try to feel my way through a story: what I am writing needs to feel true or I know I took a wrong turn somewhere.

We know you have a good relationship with other YA authors and that you share a working studio with Cassandra Clare. How does it influence your way of working? Do you help each other in some parts of the writing process?

I find it hugely helpful to have writing friends who can look at my stuff, tell me when I have steered myself off-course, and also point out when the writing is going well. It really does help me be more experimental because I know that if I put down something totally crazy there will be someone there to tell me. It's also really helpful to have writing friends because we talk about the business side of being a writer. I have often found my friends to have invaluable advice when I have been in a tight spot.

You have participated in numerous anthologies of short stories like Zombies Vs Unicorns. Which difficulties do you find when writing a short story? Is it very different from the way you work with a long novel? With which kind do you feel more comfortable? 

It took me a long time to learn how to write a short story. I wrote all of Tithe before I finished a decent piece of short fiction. Now, I feel more comfortable writing short stories and see them as a place for me to experiment with ideas that might not fit into a novel or characters that I might want to revisit later. But I am still more comfortable with novels.

You are also the author of the graphic novels The Good Neighbours. Why did you choose to write this idea asa graphic novel and not as a book? 

I've loved comics for a long time and I thought that The Good Neighbors would be perfect as a comic because it's such a highly visual story. I just finished working on another graphic novel A flight of angels with Rebecca Guay, Bill Willingham and a bunch of other contributors for Vertigo Comics, so I hope to be able to continue to work on comics and graphic novels in the future.

We have read in your website that you're working on a new middle grade novel about ghosts. Can you tell us more about it? What are your upcoming projects?

The middle grade project is called Doll bones and it's a road trip story involving a creepy doll and three kids who have to bury it.