Once Sub Pop's roster broke through to the mainstream in the early '90s, its reign as America's premier independent label drew to a close, leaving Matador Records as the definitive indie label of the decade. Matador's period of greatest impact was between 1991 and 1997, which is the time that the double-disc set What's Up Matador chronicles. The budget-priced compilation is designed as both an introduction and as a collector's dream, containing one disc called Favorite Tracks and one disc of unreleased songs. Matador didn't have a signature sound, preferring to cultivate a loose aesthetic that permitted its artists to do whatever the hell they wanted. So, there's the nervous punk of Superchunk, the jangling pop of Bettie Serveert, the fractured pop of Pavement, pure weirdness from the Frogs, mathematical rock from Chavez, disco from the Pizzicato Five, the avant rock of Silkworm, hardcore punk from Unsane, psycho-blues from the Jon Spencer Blues Explosion and Railroad Jerk, and lo-fi from Guided By Voices and Spoon, along with singer/songwriters like Liz Phair, Helium's Mary Timony, Cat Power, and Barbra Manning/SF Seals. It's an eclectic roster, but it's a rich one, containing many of the best and most important bands of the decade. The first disc runs through the hits quite effectively; for anyone curious about Matador specifically and American indie rock in general, it's an excellent primer. The second disc is for collectors and fanatics, and it does not disappoint. Many of the bands on disc one contribute unreleased songs that never sound like throwaways, and some of the label's newer bands that didn't make the first disc -- Run On, The For Carnation, and Bardo Pond -- are included. With its abundance of strong music and its complete Matador discography, What's Up Matador is an essential purchase for anyone curious about '90s indie rock.