I also adapted Richard_Chilton's
setting summary into a bullet-point format:
The Dresden Files
A series of urban fantasy novels set in a world much like our own.
Features various fantasy elements added from a variety of sources
Mortals are Ignorant
The vast majority of people in this world are normal humans:
They don't believe in magic and when they see it they rationalize it as something else.
There is no supernatural force behind this, merely humanity's need to see the world in rational terms.
Mortals are Dangerous
Involving normal humans in a supernatural struggle is often called "going nuclear" because of the risks.
Were mortal authorities made aware of the supernatural, humanity would likely declare war on them.
Human players and supernatural creatures alike respect and fear the threat of an angry mob.
That said, most cities have a handful of cops (or other people) aware of the supernatural, who deal with how it affects the rest of the world.
Supernatural Players:
full-blown wizards
sorcerers
people with minor talents
otherwise normal people with Faith-driven powers
at least three different kinds of vampires
ghouls
werewolves
fairies
supernatural halfbreeds
Note: all "full-powered" wizards are part of the White Council. This council has declared that there are seven laws of magic which they enforce on all humans that use magic.
The Nevernever:
A magical world that exists along with this one, but doesn't map directly to the real world
Changes slowly over time; only experimentation can reveal what is on the other side of the barrier.
Can be entered by wizards, some sorcerers and minor talents, some monsters, and occasionally by accident.
Contains fairy kingdoms, spirits, monsters, demons, goblins, and anything else you can imagine.
Fairies
Most live in the Nevernever, but some minor ones live in the real world.
Broken into Summer Court, Winter Court, and "Other" (called Wyldfae)
The most powerful fairies can't harm you unless you've entered into a deal with someone from fairy.
Halfbreeds
Virtually everything that lives in the Nevernever can interbreed with humans.
The majority of these offspring are fairy half-breeds (Changelings): will have to eventually choose to either A) live as a normal person (giving up all their fairy powers) or B) become a full fairy (giving up their humanity and the bulk of their free will).
Other halfbreeds are called Scions, and can come from a variety of supernatural creatures.
Unseelie Accords
One of the reasons that humanity can remain ignorant of the various things out there.
Most of the powerful groups of creatures have agreed to police their own.
Each group has total say over its own membership and defines how they can peacefully co-exist.
Most of it boils down to ignoring each other and letting every group get on with what they do.
There are rules in there for duels, self defense, paying a wergild to settle transgressions, and what is a legitimate reason for war.
Important: there is no spirit of the rules, only the letter: some will twist the accord any way they can.
Signatories include: both fairy courts, the White Council (a.k.a. the wizards), three vampire groups, and several Dragons.
As an example of how the Accords work, in the early Dresden books the hero (Harry Dresden, a wizard of the White Council) knows that there is a group of vampires in his city but cannot do anything about it unless they cross certain lines. He knows that he could battle them but if he attacked them outside of what is allowed by the Accords he would risk starting a war between the vampires and the White Council.
Old World Manners
Oddly enough, most of the 'refined' monster types (vampires, fairies, etc) respect these.
If you are an acknowledged guest they won't attack you.
If they give you their word then they will keep it.
You can usually avoid a fight by being polite and staying out of their way.
Into this mix comes your PCs. You get to pick your template and powers and then join in the fun. Odds are you won't want normal people to know about any powers you have, but there are enough weird things out there that you won't feel alone. While some gaming groups might have a different focus, the setting assumes that you will be one of the people trying to keep the world safe from dark forces while keeping humanity ignorant of the things that go bump in the night.