Gangsta rapper Tupac Shakur is shot to death in Las Vegas. The British pop group Oasis stirs international speculation about whether or not it is breaking up. When pop music makes headlines, many people are forced to admit that they have lost track of it. Herewith, a guide. Although pop music has grown more complicated, most current performers continue to recombine elements from the '50s, '60s, and '70s--sometimes literally (sampling, a technique crucial to many current pop genres, involves lifting passages from older recordings and using them in new ones). "Rock 'n' roll is here to stay," proclaimed Danny and the Juniors in 1958, and it turned out they were right.

In rock 'n' roll's first decade, songwriters like Chuck Berry and Buddy Holly established its song forms and subject matter: the lives, loves, and modest rebellions of newly enfranchised teens. Performers like Elvis Presley, Little Richard, and Jerry Lee Lewis supplied sexual charisma, abandon, and even menace. Vocal-harmony groups (do-wop) from the Northeast and Midwest prefigured the style that Motown would soon codify as "soul," while Nashville's Everly Brothers anticipated folk-rock.

Refracted through a British prism, these styles became Merseybeat, the sound of the Beatles. Bob Dylan and The Byrds expanded rock's themes to include the poetic and the political, while Eastern influences and psychedelic drugs changed the music and the culture. The '60s also saw the invention of art rock, which ranged from the minimalism of the Velvet Underground to the florid romanticism of Yes. Such music was meant for albums, not singles, which meant the decline of the medium that had previously held youth-culture music together: Top 40 radio.

I n the '70s, blues rock (a modern white version of the blues) transformed itself into heavy metal, typified by Led Zeppelin. Singer/songwriters like James Taylor recorded easy-listening confessionals, and country-rockers like the Eagles institutionalized The Byrds' country experiments (and adumbrated the slick contemporary country sound of Nashville stars like Garth Brooks). Funk (James Brown, Sly and the Family Stone, Funkedelic) made soul wilder and looser, and disco combined the celebration of Eros and dancing with beats derived from funk, Latin music, and German experimentalists like Kraftwerk. Spacey electronic music left the conservatory, and Brian Eno's Discreet Music introduced the muted wallpaper music described as "ambient."

At the same time, punk arose in reaction to art-rock pomposity and singer/songwriter narcissism, and reintroduced political content, derived from both '60s rock and Jamaican-born reggae. By the end of the decade, punk and disco were tentatively crossbreeding.

Alternative rock, which grew out of punk, refers to any band that was nurtured by the underground infrastructure (indie labels, college radio stations, new-music clubs). Alternative's commercial breakthrough came with Nirvana's album Nevermind (1991). The band's grunge formula, captured in "Smells Like Teen Spirit," combines woozy psychedelic-metal verses with explosive punk choruses. The recipe has been adopted by scores of bands; most notable: chart-topping Smashing Pumpkins' more grandiose version.

T o the uninitiated, pop music's most mysterious form is hip-hop, or rap. That's intentional: Its shifting styles and private language are designed to exclude. But hip-hop is derivative, too. Its origins can be found in African-American oral culture. Early hip-hop was mostly party music, but it developed a political message through groups like Public Enemy. Tracks like P.E.'s "Bring the Noise" gave hip-hop the urgency of an air-raid siren. The band's black-nationalist stance was followed by forays into anti-Semitism, misogyny, and anti-white racism.

Public Enemy was eclipsed by gangsta rap, which glorifies "Thug Life" (as it was deemed by Tupac Shakur). Gangsta rap's attitude is disturbing, but it's mostly escapist entertainment, rooted as much in the blaxploitation movies of the early '70s as in reality. Gangsta rap shifted hip-hop's center of gravity from the East Coast to the West Coast, and supplanted Public Enemy's machine-gun attack with a cooler, jazzier style. Coolio's 1995 hit, "Gangsta's Paradise," may celebrate "see[ing] myself in the pistol smoke," but musically, it's relaxed and sauntering. The big hit of the Fugees is a remake of "Killing Me Softly," Robert Flack's 1973 easy-listening tune.

Rage Against the Machine, a popular political rock band, derives its beats from hip-hop. Songs like "People of the Sun," which endorses the Zapatista rebels, marry hip-hop's thump, punk's wiriness, and heavy metal's roar. Hip-hop also influences the burgeoning field of electronic pop, which ranges from pounding dance music that is little more than rhythm to quietly rippling music that's only slightly removed from New Age sound. Current underground sensation Cibo Matto offers yet another variation on hip-hop with playful Japanese-accented commentary on American food in "Know Your Chicken."

I n Britain, electronic music draws on Germanic disco, hip-hop, and dub, the stripped-down, heavily echoed instrumental variant of reggae. The array of electronic styles pioneered or embraced in the United Kingdom--techno, acid house, jungle, ambient house, trip-hop, and so on--features insistent beats and wide-ranging eclecticism. Add the shrill vocals of former Sex Pistol John Lydon, and the result is Leftfield's hectoring "Open Up." Drench a track in shadowy atmosphere, and the result is the ominous soundscape of Tricky's "Aftermath." Combine '50s "space" music, French pop balladeering, and Marxist catch phrases, and the result is such Stereolab confections as "Motoroller Scalatron." Transpose the cyclical rhythms of dance music (and work by minimalist composers like Steve Reich) to guitars, and the result is the hypnotic disorientation of My Bloody Valentine's "Soon." Include reggae rhythms and quotations from Indian and Arabic music, and the result is the ethno-techno of Loop Guru tracks like "Sheikh."