Arcane Power is one in a series of class-focused supplement books released by Wizards of the Coast for Dungeons & Dragons 4th Edition. As the name says, the book is all about expanding options for the Arcane classes from the first two Player's Handbooks - Warlock, Wizard, Bard, and Sorcerer - as well as the Swordmage from the Forgotten Realms Player's Handbook. Alas, it came out before the Eberron Player's Handbook, so the Artificer isn't included, and the rise of Essentials and its subsequent killing off of all AEDU System content meant that an Arcane Power 2 never arrived, so the Artificer was left with only a few bonus content articles in Dragon Magazine.
For the five classes it does cover, Arcane Power is full of goodies, in the form of new spells, variant class features, Paragon Paths, Epic Destinies, feats, and other miscellaneous upgrades, like the Familiars rules. Equivalent books for the other sources were Divine Power, Martial Power, Primal Power and Psionic Power.