Methods for selecting advertisements to serve to a client requesting a primary webpage is provided. The client displays a referring webpage having a hyperlink to the primary webpage. Upon selection of the hyperlink, the client sends a request to a content server storing the primary webpage, the request including a referrer of the primary webpage comprising a URL address of the referring webpage. The content server sends the primary webpage to the client which includes the referrer and an advertisement request mechanism configured to make an advertisement request to an advertisement server and attach the referrer to the advertisement request. The advertisement server uses the referrer to select one or more advertisements to serve to the client. The referrer may comprise one or more search query terms submitted by the client. The advertisement server may also use the content of the primary webpage to select the one or more advertisements.