http://tvtropes.org/pmwiki/pmwiki.php/Literature/YoungWizards

Fairest and fallen, greetings and defiance!

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An ongoing series of novels by Diane Duane (the first of which was published in 1983), set in a fictional analogue of the modern world where wizards are champions of "The Powers That Be" and given the ability to rewrite the universe using the Speech — essentially reprogramming the universe and thus performing wizardry. Wizards can literally be anything (animals, robots, etc.) and can talk to anything. No, seriously, anything.

Their main duty is to travel through time and space to battle the Lone Power, the evil Power who created Entropy and Death, usually involving them heroically sacrificing their lives. (In fact, halfway through the first novel it is explicitly stated that someone usually has to die this way in order to defeat the Lone Power — although it doesn't have to be a wizard.)

Notable because magic is presented as an advanced scientific principle, rather similar to the way Fullmetal Alchemist presents its alchemy. The series also includes lots of extraterrestrials, trips to other planets and moons, and a tendency to explain all mythology as being representative or descriptive of the actions of wizards and the Powers and all language as having been evolved from a natural innate ability to "speak" the Speech. This has the effect of making the YW series feel a lot more like a hybrid of semi-hard Science Fiction and mystic fantasy than it does pure action-adventure fantasy.

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The books in the main series are:

So You Want To Be A Wizard (1983): Nita Callahan and Kit Rodriguez become wizards and must use their newfound abilities to defend New York City, Earth, and possibly even the Universe itself from a supernatural threat. Deep Wizardry (1985): Nita and Kit discover that non-humans can be wizards too, and must work with Cetacean (whale) wizards to defeat a scheme to devastate the Eastern Seaboard of the United States. High Wizardry (1990): Nita's precocious little sister Dairine becomes a wizard, and major fireworks ensue. A Wizard Abroad (1993): Nita travels to Ireland and finds out that wizardry is somewhat different there than in the United States. The Wizard's Dilemma (2001): Nita's mother develops a serious illness, and Nita enters dangerous wizardly waters in search of a cure. A Wizard Alone (2002): Nita and Kit must find a way to help a new Wizard, who is autistic, complete his wizardly "Ordeal" and gain full access to his abilities. Wizard's Holiday (2003): Nita and Kit go on "vacation" to an alien world which turns out to have a unique and knotty problem; meanwhile, back on Earth, Dairine has to cope with three alien "exchange student" wizards who have come to visit. Wizards at War (2005): A new danger appears, threatening all of Wizardry itself. Nita and Kit and Dairine gather all the other young wizards they've met, as well as some new ones, to find a way to restore the power of Wizardry before it's too late. A Wizard of Mars (2010): There may be signs of life on Mars, but while investigating, Kit begins to act strangely. Games Wizards Play (2016): Nita, Kit and Dairine coach contestants in a wizardly contest to win a year-long apprenticeship with Earth's Planetary Wizard, but all does not go as planned.

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The first nine books were rereleased as New Millennium editions from 2012-2019, creating a more cohesive timeline among other changes.

In the years-long gap between the publication A Wizard of Mars and Games Wizards Play, three shorter pieces were written and published digitally though Duane's own website, collected in 2015 for both digital and online-only print-on-demand in the volume Interim Erranty. They form a holiday trilogy being set around Halloween, Christmas and Valentine's Day respectively. They include:

Not On My Patch - It's Halloween, a day where many wizards can get away with flaunting a little magic in the open, and after what had been a rough year, Nita, Dairine and her Dad decide to have a proper Halloween celebration. It's fallen to Nita to carve the pumpkin...a rather misshapen specimen her father brought home. She ends up having a philosophical discussion with the pumpkin about its opinion on the matter, and then in a bout of odd sentimentality, decides to bring it with her trick-or-treating. Joined by Kit and Ronan, they hit the streets and visit Tom and Carl's neighborhood haunted house. All and all, a great evening, until the pumpkin starts feeling something very wrong happening in its home patch...

How Lovely Are Thy Branches: A Young Wizards Christmas - Thanks to a record-breaking blizzard, a two-day party (including epic sleepover) takes place at the Rodriguez house, during which Carmela finally manages to grant a long-held wish of her best wizardly friend, the tree-shaped Filif, by getting him fully decked out in Christmas decorations.

Lifeboats - Kit, Nita, Dairine and Rolan (among others) are called upon for an emergency evacuation of an entire alien race to new planets, because their moon is about to break up and the pieces will crash into the planet, in full-blown Armageddon style. Problem is, millions of the aliens almost inexplicably don't want to leave even in the face of unavoidable death and no one truly understands why. Kit, meanwhile, is fretting about Valentine's Day ( since he and Nita were promoted to Official Couple in A Wizard of Mars

A second novella collection, Interim Errantry 2: On Ordeal, released in 2017. Each story in the collection focuses on a different wizard and their first trial against the Lone Power.

Miscellaneous short stories set in the universe include:

Uptown Local (1986) - Set shortly after So You Want To Be A Wizard. Kit and Nita are bored and pester Tom for entertainment: he sends them off to go ride the New York subway. Actually, several New York's subways.

Theobroma (2007) - A side story involving none of the usual characters; instead, we're introduced to Ken, an adult, work-a-day wizard who does "agency work", consulting on problems both magical and mundane. Today's assignment: help a woman fill the sudden vacancy in her gourmet chocolate shop. Turns out her chocolate-making partner isn't the only thing that left...

There's also a sister series, Feline Wizards, which takes place in the same universe, but concerns a team of cat wizards who maintain the worldgate wizardry for New York City.

These books provide examples of: