I believe they use the same model as Google, et. al. Sponsored listings for relevant searches. edit: They also have an affiliate program when linking to eBay

I believe they use the same model as Google, et. al. Sponsored listings for relevant searches. edit: They also have an affiliate program when linking to eBay and Amazon (http://help.duckduckgo.com/customer/portal/articles/216405-advertising http://help.duckduckgo.com/customer/portal/articles/216405-a...)