Participants have 24 hours to either donate $100 to ALS research or dump a bucket of ice water over their heads, after which they're allowed to nominate three more contenders to do the same.
The idea is that the cold water causes paralysis similar to that induced by ALS, which can lead to "full muscle paralysis and respiratory failure", as "nerve cells in the brain and the spinal chord eventually degenerate and die," explains The Star. There is no known cure.
According to The ALS Association, they've received $13.3 million in donations between July 29 and August 17 with most of it coming from the challenge. Woohoo! We love it when people come together for a great cause.
Here are the top celeb ice bucket challenge videos so far... REALLY hoping President Obama accepts the Biebs' challenge! *all fingers crossed*