The ice bucket challenge was one of the most successful viral marketing campaigns ever. In 2014, people all over the world participated by dumping a bucket of ice water over their heads and challenging others to do the same, or donate money to the ALS Association. Over 17 million people participated online, raising over $115 million for ALS research. It was such a simple idea - get wet and cold or donate - but it tapped into people's natural desire to participate in trends and support good causes.