The 2011 TIME 100

It's already become a cliché to say that change is the only constant, but more than ever, we are living in an age of constant, transformative change. The Arab Spring represents a world historical cascade of events that is changing the Middle East. The earthquake and tsunami in Japan could change the history of Asia. And this season of revolutionary change has been deepened, widened and accelerated by the power of social media. It's never been easier to influence or to be influenced.

This year's TIME 100 list reflects those stories, whether from the Middle East or Asia or the world of social media. You can sometimes impute influence by reverse engineering events: Who was responsible for triggering these extraordinary movements? Wael Ghonim's plaintive posts on Facebook helped spark the Egyptian revolution. Fathi Terbil's detention helped ignite the revolt in Libya. Katsunobu Sakurai denounced the lethargy of Japanese authorities in helping earthquake victims. The artist Ai Weiwei became the conscience of China. (See the 2011 TIME 100 poll results.)

Influence is impossible to measure. It's a little like what social scientists call the butterfly effect: the idea that a tiny change in one part of a system can yield gargantuan changes later on. But often this is a romantic illusion; large-scale changes occur only when great numbers of people become restive over time, just as people in the Middle East have been moved to shake off decades of authoritarian rule.

What social media have done is to make us all more aware of what's going on — and offer a new avenue to organize opposition. We like to think revolutions rise from below, but through most of human history, it's the elites who have caused and led revolutions. Now, because of social media, anyone can communicate with everyone. We're seeing that in the Middle East, Africa and China. The democratization of information may actually lead to real democracy. (Watch "Where Do Revolutionaries, Rain and Kanye Rank on the TIME 100 Poll?")

Once again, the impresario of the TIME 100 list is assistant managing editor Radhika Jones, who did a superb job of putting the issue together. Our edit team orchestrated great pairings, recruiting as TIME 100 writers Barack Obama, Rush Limbaugh, Arnold Schwarzenegger and Helen Mirren. Senior art director Emily Crawford gave the issue a new, sprightly design, and associate picture editor Natalie Matutschovsky arranged to photograph Ghonim in Cairo — and "tiger mom" Amy Chua in her daughter's bedroom ... with live tigers.

Watch "TIME 100: Haiti Revisited."

See TIME's Pictures of the Week.