"DuckDuckGo gets its results from over 50 sources, including DuckDuckBot (our own crawler), crowd-sourced sites (in our own index), Yahoo! BOSS, embed.ly, WolframAlpha, EntireWeb, Bing & Blekko. For any given search, there is usually a vertical search engine out there that does a better job at answering it than a general search engine. Our long-term goal is to get you information from that best source, ideally in instant answer form."

source: http://help.duckduckgo.com/customer/portal/articles/216399-s...