the ice bucket challenge

You've probably seen a good number of photos this week of the rich and famous dumping buckets of ice water over their heads. Here's why.

Everyone you've seen is participating in the Ice Bucket Challenge. The challenge involves daring a person to dump a bucket of ice water over their head within the next 24 hours, or else donate money — usually $100 — toward fighting ALS. Even if a person completes the challenge, they're more than welcome to donate money too.

Once a person completes the challenge, they're also supposed to dare several other people — usually three — to participate, which is why the challenge has been growing and growing.

The ALS Association says that Pete Frates, a former Boston College baseball player, began the Ice Bucket Challenge — and he's being widely credited for kicking it off. Frates is 29 and has been living with ALS since 2012. As Slate notes, however, it's not entirely accurate to credit Frates with beginning the challenge. Several people actually took the challenge before Frates, at which point they were only supposed to donate to a charity of their choice, rather than the ALS Association specifically. That said, the challenge has really become a phenomenon since Frates took the challenge at the end of last month.

A lot of people — and a lot of famous people too. The latest trend is for tech executives to take it on: we've seen Mark Zuckerberg, Satya Nadella, Phil Schiller, and Dick Costolo in just the past day. But it's far more than that. Justin Timberlake, Jimmy Fallon, The Roots, Matt Lauer, Martha Stewart, and Chris Christie are among the others who have accepted, dunked themselves, and challenged others. President Obama has apparently declined to get soaked, and is instead making a donation.

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Bill Gates answers the challenge.