For the uninitiated, Pathfinder is a fantasy role-playing game created by Paizo Publishing that is the spiritual (and in my humble opinion literal) successor to Wizards of The Coast's Dungeons and Dragons version 3.5.
Since it's inception in 2008 it has become my game system of choice and while I could write a bunch about why that is, talking about the different directions that the two companies took and comparing the rule systems themselves, I'm not going to do that... right now I want to talk about Adventure Paths.

Almost all role-playing games I've had the pleasure of playing (or at the very least reading through) have pre-written adventures in one form or another. These usually take the shape of short stories, missions or quests that take you through a couple of levels (or the appropriate equivalent for non level based games) and are meant to familiarize beginners, be they player or gamemaster, with the system in question.
While these adventures are really useful and a great way to get into a new game system, for gamemasters who have trouble coming up with their own campaigns (like myself) this is never enough.

...enter the Adventure Paths!

Adventure Paths are basically fully written pre-generated campaigns that take your characters through their whole adventuring careers... from zero to hero if you will
They start you off at level 1 and usually end between level 15 and 17 (although some take you as far as level 20... the maximum in Pathfinder).

APs (as they are sometimes called) first appeared in the late days of D&D 3.5 as interconnected adventures that were released sequentially in Dungeon magazine.
Three APs were published under the auspices of Wizards of The Coast, these were "Shackled City", "Age of Worms" and "Savage Tide" and they were freaking awesome!

Shackled City has your characters begin in a town built in the caldera of a dormant volcano (krhm, khmm... foreshadowing much?), has them face of against a secret society led by a vile fiend, sends them to a layer of the Abyss (a dimension of sorts) created from the carcass of a powerful hag, only to eventually pit them against a fallen angel who had gone mad from centuries of imprisonment.

Savage Tide sends your characters on a long sea voyage that takes them to a far off tropical island swarming with dinosaurs and wild beasts but also much darker and more dangerous creatures. It has them use their brains or their brawn (or both) in order to maneuver past the various feral locals and ends on an appropriately badass note... fighting the avatar of a Demon Lord that's trying to claw his way to their plane of existance.

Like I said... AWESOME!

The "Age of Worms" Adventure Path, which I haven't played personally, also has an appropriately epic storyline. One that ends in a fight with the dark demigod of worms and the undead Kyuss. Interestingly enough, the very same demigod that inspired the name of the american stoner rock band Kyuss, a band that would later on split up and form The Queens of The Stone Age.

After publishing these three APs Wizards of The Coast would go on to make the fourth edition of Dungeons & Dragons, thereby changing the entire rules system and to a lesser extent the way they publish written adventures, while the newfangled Pathfinder RPG took over the format of Adventure Paths (they even tried to trademark the term "Adventure Path") and continued churning out whole campaigns to this day.

So far there have been 18 Adventure Paths published by Paizo (of which I've played roughly half) and more are in the making. I plan on going through most of them (if not all of them) at a later time, so if this text tickled your fancy or intrigued you in any way, keep an eye out for more posts in the future