Feeds provide the backbone of data exchange for mashups. Many web sites—including Flickr—generate feeds, particularly in the RSS and Atom formats. In this chapter, you learned about the ecosystem that has arisen around this plethora of feeds: news aggregators that gather feeds for reading, validators that help you produce good feeds, scrapers that let you generate feeds when a web site doesn’t provide one, and remixing tools that let you generate elaborate mashups of feeds. In an extended example of mashups based on feeds, I showed how to use Yahoo! Pipes to generate a single topical news feed that is a mashup of several other appropriately filtered feeds.