Write one book, and you can feel confident in calling yourself an author. Write three, and you might make a career out of it yet. Write a dozen, interconnected and following a common thread of over-arching plot, and you just might be a fantasy author.

What is it about writing series of books? Can’t anyone just write a single fantasy book anymore?

Of course they can, and many do, but fantasy is a ripe market for series readers and writers.

Why does fantasy work so well as a series?

It comes down to worldbuilding, mostly. It’s a lot of work for both the reader and the author to learn all the ins and outs of a fantasy world. The more it differs from Earth, the deeper and more expansive the scope, the more time and effort go into that learning process. Starting that over again every book can get tedious, and keeping things in the same universe allow for the author and reader to jump into the meat of the next story with less preamble.

How long is “fair” between books?

Here’s one of the major hangups with in-process series. If no one reads the first book, a publisher (even a discouraged self-publisher) might pull the plug before any of the rest gets written. But that leads to fans stuck waiting to find out what comes next. Are you a fan of Brandon Sanderson (a notoriously fast writer)? Great! Not long for you until the next installment comes out. Are you caught up on George R.R. Martin or Patrick Rothfuss (less prolific authors)? Well, you’re in for a wait.

Of course slow writers wish they put out books more often; they’d catch less grief from fans. But they have a process, a workflor, and other commitments that limit their rates of writing. Would we still love those series if they came out quicker, but less immersive. Do the extra years of work make a difference, or is it just polishing shirt buttons and straightening the pictures on the wall? We’ll probably never going to find out, because it’s unlikely that these authors are going to change their habits.

So if you’re the sort of person who gets irritated by unfinished series, maybe you should stick to reading ones that are complete. Decide for yourself if the aggravation of waiting between books is worth more than the feeling of being left out of the latest release of an unfinished series.

What are the challenges of a long series?

I can think of three main pitfalls that get worse the longer a series goes on:

1. Maintaining consistency – Those inconvenient decisions early on can handcuff you in later books. Why did you have your MC be from X instead of Y. Maybe your recurring villain’s accent changes between book 1 and book 8. Keeping good records is key, but a bible of in-world facts can be a straightjacket as well, limiting the creative decisions available.
2. Closure or no closure? – Plots come and go in a long series. Each book should have its own arc, as well as interact with arcs from prior and subsequent books. But what can happen is that certain plot lines hang over the series like a pall. Will they or won’t they? Whatever happened to ____? Will they ever tell me what happened to the prisoner that escaped in book 3? Too much closure at any given point can make a series feel complete, and let readers off the hook to continue on. Too little, and you risk annoying them with cluttered plot threads.
3. Unlimited character growth – Your farmboy hero saved his village. Then rescued his older brother’s army platoon. After that, he saved the kingdom, became general, then inherited the kingdom. Now he’s fighting off world-ending threats two per book, and it’s starting to feel a little overdone. Avoid this problem by not advancing your character’s status or power every book. Simply having them evolve as a person can be enough, especially for a character who isn’t a raw lump of clay to begin with.

What can you do with a series that you can’t with a single book?

I could go on at length about how you can go on at length. I could even get into some of the intricacies of plots that span multiple novels. But instead I’m going to give one reason that, perhaps more than any other, determines why so many books are written as part of a series?

What can you do with a series that you can’t with a single book? Make a career.

Think of any big-name author currently writing fantasy (my primary genre). What do they have in common? They write in a series. Sometimes they have more than one going at once, but the common theme is that readers will follow a series more than an author, at least until that author makes a name for him or herself; then they’ll follow them to another series.

If stand-alone novels were the money-makers of the industry, you’d see more of those. Sure, you get successful standalones here and there, but they’re the exception to the rule. Sometimes a choice can be both a creative one and an economic one. A generation of writers have grown up reading series, and prefer them, so it’s not strictly about money. But once you’ve got a premise nailed down that your reader base loves, it can be hard to set it aside (and the royalties/advances that come with it) and move on to another.