From the publisher's website:
Arcane magic is one of the most popular, flexible, and influential components of the Pathfinder Roleplaying Game. Arcane spells immediately call to mind some of the most iconic elements of fantasy stories. Characters flying through the air, chucking bolts of lightening at their foes, and deflecting dragon’s breath with mystic shields are fun and memorable parts of high-magic games. Even in more low-key settings, characters are often summoning light, sensing magical auras, and enhancing their natural abilities with softly muttered spells. Arcane spells are the tools used in most campaigns to represent the world’s magic of combat, research, and wards of defense. A great deal of the sense of the fantastic in the Pathfinder Roleplaying Game comes from arcane magic.
Fantasy stories are also full of rogues who once trained with master wizards and retain a bit of that knowledge, bored swordsmen who happen to have vast resources available if they call on ancient pacts, wondrous magisters able to access many forms of magic, and semi-competent sorcerers with powers they barely understand and have trouble controlling. These characters can be built, at least sometimes, with the multiclassing rules and prestige classes, but such efforts often feel awkward and the mechanics may not make sense when a character’s entire backstory is taken into account. Of course in any core rulebook there is a limit to the number of character options that can be presented, and many players quickly crave more flexibility.
The Genius Guide to Arcane Archetypes provides the material necessary to give spellcasting classes new forms of arcane magic or to add arcane power to classes that normally lack it. It does this through the use of archetype packages—a way to remove a set of related class abilities normally included in a base class and replace them with new powers (in this case, tied to arcane magic). These archetype packages can change how magic works for a character (as you’ll see with the Sigil Mage and Shadow Master archetypes) or add an element of arcane spellcasting to a character that normally lacks it (with archetypes such as the Hedge Wizard and Warder).