How to write fantasy

You have a world with something impossible in it and a decision to make before chapter one: which fantasy are you writing, and what does that label promise the reader? Fantasy is a big tent, and the tent's entrances are labeled. This guide covers what the genre itself commits you to, how to choose among its subgenres, the world rules all of them demand, and the bookkeeping that keeps a long series coherent.

What makes fantasy fantasy

Wikipedia's article on fantasy literature defines the genre as "literature set in an imaginary universe, often but not always without any locations, events, or people from the real world", and places it within speculative fiction, distinguished from science fiction and horror "by the absence of scientific or macabre themes, respectively, though these may overlap". Underneath the definition sits the working craft fact: in fantasy, the impossible is accepted. The dragon is not a hoax awaiting debunking and the spell is not an anomaly awaiting a rational explanation. The story treats the impossible as real and asks what people do inside a world where it works.

That is the line against the genre's neighbors. Horror treats the impossible as a breach; magical realism treats it as furniture; fantasy builds a world that runs on it and puts the drama on the people.

The subgenre choice is a promise

The label you shelve under is a contract about scale, tone and how magic behaves:

• [High fantasy](/glossary/high-fantasy) promises a fully invented secondary world, mythic tone and epic stakes, with magic and the nonhuman usually positive, wonder-bearing forces rather than priced ones.
• [Low fantasy](/glossary/low-fantasy) is defined negatively: magic is rare or marginal in an otherwise mundane, human-dominated world, and its intrusion is the story.
• [Urban fantasy](/glossary/urban-fantasy) puts magic in the modern real-world city and gives the protagonist a foot in both worlds, usually borrowing noir and police-procedural furniture along the way.
• [Sword and sorcery](/glossary/sword-and-sorcery) promises personal-scale violent adventure with morally gray heroes, and, unlike grimdark, the hero usually still wins.
• [Dark fantasy](/glossary/dark-fantasy) shades toward horror: dangerous worlds, costly magic, unsettling atmosphere.
• [Romantasy](/glossary/romantasy) makes the fantasy world and the romance structurally interdependent, and inherits romance's ending contract with them.

None of these is a quality ranking. They tell the reader what to audit: the high fantasy reader audits scope and wonder, the low fantasy reader audits what the intrusion costs, the urban fantasy reader audits two worlds' rules at once. Pick the shelf deliberately, because readers use it to decide what your book owes them.

World rules and their costs

Accepting the impossible is not the same as making it arbitrary. Fantasy readers accept dragons and then audit dragons: what they can do, what it costs, what kills them. The pattern holds even outside prose fiction. Wikipedia's article on magic systems, which covers games rather than novels, still defines the subject by "the rules, limitations, abilities, and characteristics" that define how magic works. Those are the same three tests your readers will apply: rules, limitations, costs.

The catalog's working tools for this are Sanderson's laws on why limitations matter more than powers, Magic A is magic A on why a stated rule binds the whole story, and the discipline of designing costs and limits before the plot needs them. Then write the rules down: what power can do, what it spends, what it cannot touch. A rule you have not written is a rule you will contradict, and fantasy readers keep receipts across volumes.

One dial worth setting early: how explained the magic is. Tolkien's magic stays mostly unexplained and carries wonder; hard-magic systems put rules on the page so readers can anticipate solutions. Both work. Switching between them mid-series usually does not.

Canon across a long fantasy

Fantasy is the heaviest worldbuilding genre and its series run longest, which makes canon the genre's real operating cost. A realm named in book one is an arc in book four; a bloodline, a treaty or a sword's origin planted early is a debt the ending must honor. Tolkien's sub-creation explains what is at stake: a Secondary World earns belief through inner consistency, and the consistency is cumulative. The reader's belief in book seven is built from the facts of book one still holding.

That is a story bible workload: world rules with their history, character states, who knows what, what was promised. Fantasy punishes improvisation harder than its neighbors, precisely because it promised more at the door.