POTW: Lady Gaga, Perez Hilton, Justin Bieber, Katy Perry
Billboard's BBF Juanes played a track from his new album, the aptly-titled "P.A.R.C.E." (which is Colombian slang for "friend") for the Billboard staff in New York on Dec. 8.

"(Billboard's Latin Songs chart) is the beat of the industry," says songwriter Omar Alfanno, who penned Son by Four's "A Puro Dolor," the longest-running No. 1 track in the history of the chart (61 total weeks, 20 at No. 1). "If you're not on that chart, you're nowhere. As composers, we don't write to be outside of the chart. We have to write songs that are worthy and precise." Although on Oct. 8, 1994, Billboard launched subgenre airplay charts - regional Mexican, Latin pop and tropical - Latin Songs continued to be the holy grail. Its importance only grew when in November of that same year, the chart switched to Nielsen BDS-monitored airplay. While tracks were initially monitored by their number of plays, on Aug. 30, 1997, the chart switched to audience impressions, cross-referencing the time of play with estimated listeners, according to Arbitron data.

Looking back at the chart's top songs through the years, it's uncanny how they reflect both the musical and demographic landscape. "It's the national chart," Sony Music U.S. Latin president Ruben Leyva says. "It's the only true reflection from a national perspective taking into account all the genres." Following a clear Mexican dominance with acts like Juan Gabriel, Ana Gabriel and Daniela Romo topping year-end charts, the early '90s saw a boom of Tejano music, with La Mafia and Selena topping the year-end chart from 1993 to 1996.

Tejano and Mexican acts continued to dominate the charts through the '90s, but by the end of the decade a new generation of artists-many of them Puerto Rican-began to climb regularly to the top 10. By the early 2000s, the chart was all about variety, with an increasing number of appearances by names from Colombia (Shakira, Juanes, Carlos Vives), Puerto Rico (Chayanne, Ricky Martin, Huey Dunbar, Jerry Rivera) and also, fresh music from more traditional regional Mexican acts like Conjunto Primavera, Los Tigres del Norte and Banda el Recodo.

Reggaeton stars Wisin Y Yandel's second of eight Latin Songs No. 1s, 2006's "Pam Pam."

The biggest milestone from a musical standpoint, however, came in 2003 and 2004, with the advent of reggaetón. "That opened the door to a new genre of music," CBS Radio VP of Latin programming Pio Ferro says. "The Latin rhythmic sound is so crossover, it just broadened the spectrum." On Aug. 13, 2005, Billboard launched its Latin Rhythm Songs chart, incorporating a breadth of music that went far beyond reggaetón and continues dominating the chart today. "The urban movement revolutionized U.S. radio and forced stations to change the format," says Walter Kolm, former president of Universal Music Latino/Machete. He now manages singer Cristina Castro. Kolm experimented early on with pairing urban and pop acts, delivering tracks to radio that were far more youth-leaning and uptempo than the ballads of yore.

The move came at a time when research became more refined. No longer, some say, was radio programming a reflection of what labels pushed, but rather, of what research dictated. That trend only accelerated with the advent of the Portable People Meter as a ratings tool in 2008. Now, says one executive who prefers to remain nameless, "we have a less politicized chart. It's a truer representation than it was 10-15 years ago. There is PPM accountability and people themselves are telling us what we should be playing." Today there are 119 stations that report to the Latin Songs chart, and 325 songs have hit No. 1 during the past 25 years.

So, what's hot now, according to the chart?

A mix of traditional Mexican music, home-grown urban and pop tracks and some English-language hits, reflecting an increasingly diverse audience that includes younger, U.S.-born Latinos who are now tuning in to what used to be only their parents' radio stations. "As more Latinos assimilate, and they're proud of their roots, it's not anti-cool to listen to Spanish music," Ferro says. "Everything is cyclical, and it's pretty uptempo now. But we're going to see more no-name artists becoming big-name artists because it's easier to record things that may catch fire."

Regardless of what's playing, Kolm says, "the chart is more important than ever now. Because selling tickets is more important, and tickets get sold when an artist is hot on the radio. And for the business in Latin America, beyond being the most trustworthy chart, it's the one that sets the trends. Most charts in Latin America follow the Billboard chart. That's why it's so important to reach No. 1."

Chart data provided by Billboard director of charts Silvio Pietroluongo, associate director of charts/radio and Chart Beat columnist Gary Trust and Latin/R&B/hip-hop chart manager Karinah Santiago. See this week's issue (Oct. 8) for more interviews with the format's top superstars and tastemakers.