In the 10 years since the publication of Cassandra Clare’s City of Bones, Clare and her editor, Karen Wojtyla, have worked together to build a world that’s captivated millions of readers. With 50 million copies in print, a forthcoming 10th anniversary edition of City of Bones releasing in November, and Lord of Shadows, second in the Dark Artifices series (chronologically third in the Shadowhunter Chronicles and the sequel to the Mortal Instruments series), hitting shelves this week, Clare and Wojytla spoke with PW about their relationship, keeping track of the vast Shadowhunters world, and creating a cohesive fantasy universe.

It’s been a decade since the publication of City of Bones. How have you both changed, as a writer and an editor, over the past 10 years?

Cassandra Clare: The biggest challenge of writing a first novel is not knowing if you can write a novel. Once you complete one book, you know you can do it, but each novel after that presents its own set of challenges. I’m constantly learning about story structure, ever-more effective writing and characterization. I certainly hope I’ve improved, but I always want to be learning new things and setting myself new challenges.

Karen Wojtyla: I don't think I’ve changed that much as an editor. Perhaps I’m a little more decisive about what I like and what I think will work. I’ve always liked the variety of what I do and perhaps I appreciate that even more now.

CC: I can only speak from my own perspective as an editee, but I do think that Karen’s confidence in editing urban fantasy has grown over the years.

KW: Well, I do think you grow and learn and as your experience broadens, it deepens your understanding of structure and technique, which really does make you a more effective editor.

Cassie, you’ve collaborated with authors, including Robin Wasserman, Sarah Rees Brennan, Maureen Johnson, and your husband, Joshua Lewis, to write companion novels set in the world of the Shadowhunters. What is the experience of sharing creative control of the Shadowhunter world like? Do you ever find aspects of co-writing within a world you created difficult?

CC: There are times when I want to be in control of the whole fictional universe, and there are times when I really enjoy sharing a fictional place with somebody else. It’s very satisfying to untangle a knotty fictional problem on your own, but it’s also really nice to have someone else around to come up with ideas that you never would have had.

I’ve spent a lot of time with Josh, Holly, Maureen, Sarah, and Robin, and we’re all pretty used to working together, so we haven’t run into any major disagreements yet.

Karen, how did you come to be a children’s and YA editor?

KW: I’ve always loved the directness and clarity of writing for children and teens. These are readers who really care about what they’re reading, for whom books can make a real and lasting difference. I love being part of that.

You’ve edited a diverse list of books, from YA and middle grade authors like Cassandra to board book authors like Karen Katz. When considering a book to add to your list, what do you look for?

KW: Voice. Atmosphere. Great dialogue. Vividly realized characters. But always a unique voice or vision.

When you acquired the Mortal Instruments trilogy more than a decade ago, what was it that hooked you?

KW: I was hooked by about page two! The opening scene was so bold, and seemed so utterly real to New York and to those teens. It was so naturalistic for a fantasy, it felt immediately, compellingly realistic. But with demons—an unbeatable combination!

The world of the Shadowhunters is immense, now populated by countless characters and multiple time periods. How do you both keep track of these many threads to ensure consistency and continuity?

CC: It can get confusing! I keep detailed notes on families and on the timeline, and I frequently refer to the Shadowhunter’s Codex. It’s very convenient to have a reference book about the world I created.

KW: Well, I try! Fans will tell us if we slip up. I take loads and loads of notes as I read successive drafts: handwritten, with lots of asterisks and arrows and underlining—on characters, locations, timeline, plots and subplots, etc.

CC: That’s a good point, Karen—we’re very hands on. Most people do their edits in Track Changes now, but we still use printed versions of the books and make changes on the page. This leads to a lot of situations where Karen is chasing me around to turn in a massive stack of paper, but it also gives the books a more organic feel.

KW: Massive stacks of paper indeed! But I think Cassie is right, there’s so much to think about and it’s so interrelated that working physically on paper is an asset for us.

How would you characterize your relationship? How has collaborating for so many years changed how you work together?

KW: I think it’s more comfortable. She can leave scenes TK in early drafts and I know I’m in for something great—even if it might be upsetting, it will be good! We trust each other a lot and I have tremendous respect for Cassie’s skill as a storyteller.

CC: I also have tremendous respect for Karen. She really knows how to take rough material and refine it. I feel lucky and privileged to have worked with her for 12 years. Karen has been instrumental in my growth as a writer. She challenges me and encourages me to avoid repeating characters and themes, and to always bring something fresh to the Shadowhunter world. Karen is one of the few people as invested in the Shadowhunter world as I am, so she has thoughts about everything, even down to what kind of shampoo a character might use, and whether it fits with their personality.

KW: Hmmm, that makes me feel like I may get a little too into details.... But I’ll turn that one back on Cassie and say she creates characters who feel so alive and defined as persons that I really do think about whether some particular words or actions—or shampoo I guess!—are true to that person.

What have been some of the challenges of creating a cohesive fantasy world?

CC: The foundation of every fantasy world is the same as that of every book’s world. The characters must feel real and relatable, and face conflicts that feel true to life, even if there are demons and warlocks and faeries involved. That core relatability is what allows readers to suspend disbelief and enjoy the magic of the world you’re creating. The world must also feel fresh yet recognizable—a new spin on old folklore is difficult but key.

KW: I think it’s also keeping the magic grounded and having it all linked. Never saying, “Oh, it’s magic, it doesn’t need logic.” It always does.

CC: Absolutely. A magic system should be consistent and balanced. There should always be consequences so that magic isn’t a get-out-of-jail-free card for every situation. Years ago Karen and I discussed a shape-shifting rune, and we decided that it would never work, because it was overpowered. There would never be a situation where a reader wouldn’t think “Why didn’t they just use the shapeshifting rune?”

Trust and mutual respect is an integral part of the author/editor relationship. Can you talk about a time when you’ve had to take a leap of faith and rely on that trust and respect?

CC: When I turned in the first draft of Lord of Shadows, Karen was concerned that the villain was too removed from the lives of the protagonists. This was a villain I’d been planning on for a long time, and I didn’t want to give them up! But since I trust Karen’s opinion, I decided to create a secondary villain, one who has much more immediate personal connections to the Blackthorns and Emma. In the end, making that change and creating that villain allowed me to say things about prejudice and tolerance that I feel are important to say and truly gave the book its theme.

KW: I think as an editor you’re always relying on that trust—it’s the only way to go forward, no matter how many questions you may have for a writer, you trust their vision. Of course, it’s my job to ask those questions, and I might put my finger on a sore spot—and that’s when you are relying on that mutual respect to work things through.

The fans of the Shadowhunter books are enthusiastic and vocal. Do their hopes, demands, and concerns have any bearing on the direction of the novels or potential companion novels?

CC: I’m a big believer in outlining, and I plot my novels before I start writing them. I love hearing from readers, but by the time I get their reactions, I’m already writing the next thing. That said, if characters are very beloved or surprisingly popular, I try to think of more ways to weave them into the story, and sometimes I write short pieces involving them.

How has the reader response evolved over the past decade? Can you share any highlights from the 10th anniversary celebration of City of Bones?

KW: Fans are more involved and committed with every book. It’s absolutely amazing to get here—10 years! I’m delighted that fans continue to be hugely engaged. We’re publishing a 10th anniversary edition, especially for them, with lots of new art and extra content. It feels like a major milestone to look back and celebrate. And to look forward to lots more!

CC: Obviously the internet has changed things a great deal over the past 10 years. Fans can connect with each other more easily and much faster than before, and there are also more opportunities for me to connect with my fans who live great distances away. Reader/author interactions are very casual online, but there is something special about meeting people in person, so even though the internet has changed things, signings and meetings with fans remain a unique magic.

Lord of Shadows (The Dark Artifices #2) by Cassandra Clare. S&S/McElderry, $24.99 May 23 ISBN 978-1-4424-6840-8

City of Bones: 10th Anniversary Edition (The Mortal Instruments #1) by Cassandra Clare. S&S/McElderry, $24.99 Nov. 7 ISBN 978-1-5344-0625-4