Ad revenue. Go do a DDG search. You'll notice off to the side there is an ad conspicuously tagged as such. Click that, and DDG makes a little bit of money. From

Ad revenue. Go do a DDG search. You'll notice off to the side there is an ad conspicuously tagged as such. Click that, and DDG makes a little bit of money. From what I understand, their ads are only related to the content of the current search.