The Ice Bucket Challenge is a charity fundraiser undertaken by a number of organizations promoting awareness of amyotrophic lateral sclerosis (ALS, AKA motor neuron disease or Lou Gehrig's disease). Most donations went to either the ALS Association in the USA, or the Motor Neurone Disease Association in the UK.

The challenge was simply to have a bucket of ice water dumped over your head. While specific rules varied, it was common to stipulate that once some one challenged you, you should act on the challenge within 24 hours, you should record the event and post it on-line, and you should donate money to some ALS-related charity. In the US the most common donations seem to have been $10 if you accepted the challenge, and $100 if you declined; in the UK it was £3 if you accepted and £10 if you did not.

The challenge was introduced in the summer of 2014, and promptly went viral, with a ridiculous number of stars participating, funny or clever videos on YouTube becoming overnight sensations, and the word "challenge" becoming a common meme amplifier used higgledy-piggledy across the internet. The ALS Association reported donations of $115 million in 2014, while the total donations for 2013 had been a paltry $19.4 million. Other charities received similar spikes in donations.

While the Ice Bucket Challenge was certainly a spectacular fad, it has not completely faded out. Every summer it comes back in some form, sometimes bigger in one country or another, sometimes having a few new faces sparking a brief comeback. In 2016 the was a fad for putting interesting substances (not ice water) in the buckets. In 2017 Massachusetts governor Charlie Baker introduced a bill declaring the first week of August each year to be "Ice Bucket Challenge Week". The ALS Foundation has changed their campaign name to the "Challenge Me Campaign", and in 2019 introduced the In Your Face Challenge (#InYourFaceALS), in which people challenge each other to take a pie in their face.

In the face of the immense rush of funding, ALS organizations struggled to find ways to use all this money. While it was certainly put to good use, despite what some naysayers claim, there was a significant downside to the campaign. Many people did not increase their charitable donations, but simply took some money they would donate anyway and changed over to ALS; this is not inherently bad, but when choosing where your money should go, some famous person dumping water on their head is a bad criteria. While it is good for ALS research to be funded, it is not the most needful cause -- especially not after the first rush of donations overwhelmed the current funding needs. If you are interested in saving lives, or improving lives, a good resource is Givewell, which researches where your money is most needed and can do the most good.