It's fair to view hip-hop as the greatest musical innovation since the dawn of rock 'n' roll. After the popular breakthrough of "Rapper's Delight" in 1979, it took about two decades for the genre to dominate American culture, conquering everything from the charts to commercials to clothing stores. But for such a pervasive musical style, few useful books have been written about rap. That's a shame, because unlike jazz or rock acts, few rap artists enjoy long careers, and, though an endless stream of new talent makes and releases records, few young MCs and DJs seem aware of what came more than a few years before. Granted, hip-hop has generally been about fashion, politics, and the here and now, but it's good to know your roots. In 1984, British musician and journalist David Toop wrote what could have been the first comprehensive book about rap, DJing, and B-boy culture, Rap Attack, now made available in an expanded third edition. Toop's new preface concentrates on the diametric shift from the pop confections of Vanilla Ice and MC Hammer to hardcore gangsta rap, and the regrettable party-ending violence that ensued shortly thereafter. If there's any question as to how much hip-hop has changed over the years, the book's many pictures answer them. The snapshots documenting rap's early days are all smiles, but around 1990, the smiles are replaced by scowls and menacing poses. So what happened? All signs point to dollar signs. There's an inadvertently nostalgic quality to Toop's book: His relatively disorganized prose and the unchecked onslaught of information are indicative of the excitement of the time, a mad rush to collect all that happened (Last Poets, Watts Prophets, Sugar Hill Gang, Grandmaster Flash, Kurtis Blow, and so on) in just a short period. It's sad that once rap became lucrative, the fun was replaced by business savvy that placed commerce before art, but Toop seems to sense that the current surge of creativity in the underground may be signaling a shift back. His book admittedly has no conclusion, but the story of hip-hop itself isn't finished; Rap Attack is a history that keeps rewriting itself, an endless cycle that should keep expanding each time the circle reaches start again.