Information on the book from the web site of the author, Alice Hoffman. You can also read an excerpt from the book here.

The following is the book description:

For more than two hundred years, the Owens women had been blamed for everything that went wrong in their Massachusetts town. And Gillian and Sally endured that fate as well: As children, the sisters were forever outsiders, taunted, talked about, pointed at. Their elderly aunts almost seemed to encourage the whispers of witchery, with their musty house and their exotic concoctions and their crowd of black cats. But all Gillian and Sally wanted was to escape. One would do so by marrying, the other by running away. But the bonds they shared, even into adulthood, brought them back--almost as if by magic...

A review from Booklist:

Magic, fantasy, and full-tilt love-at-first-sight have figured in all of Hoffman's sexy, funny, and endearing novels, but they blossom as they never have before in her latest effort, a tale about four generations of Massachusetts sisters. The unusual Owens women are beautiful, with unforgettable pond-gray eyes; a blood-deep knowledge of the supernatural power of plants, animals, and storms; and pronounced sensitivity to love and evil. Sally, dark and practical, and Gillian, blond and wild, go to live with their peculiar and reclusive aunts after the death of their parents. Taunted and feared by the town's children, they long for an ordinary life far from their quirky aunts and their mysterious garden and the desperate, lovesick women who appear at their door after dark. Gillian heads for the desert and the company of dangerous men, while Sally finds love and bliss only to have her heart shattered. She flees from the scene of her tragedy with her two young daughters, works hard to achieve normalcy, and almost succeeds, but Gillian appears with a dead man in her car and the entire world reels. In Hoffman's universe, all boundaries between inner and outer realms are erased. Fear brings whipping winds, a malevolent spirit causes lilac bushes to achieve monstrous proportions, and love turns the air sweet and golden, melts butter, and makes everyone giddy. Hoffman has created a cosmic romance leavened with just the right touch of pragmatism and humor. Donna Seaman

Here are several more reviews of Practical Magic:

http://www.bostonreview.net/BR20.2/Fried.html

http://www.nytimes.com/books/97/09/14/reviews/18216.html

http://www.heall.com/books/spirituality/practicalmagic.html

http://www.bookreporter.com/reviews/0425168468.asp

http://www.theromancereader.com/hoffman-magic.html

http://www.flowerfire.com/seized/reviews/practical_magic_sara_lipowitz.html