Various techniques are disclosed for delivering contextually related advertising content to end users of a computer network. Advertiser campaign information may be accessed. In at least one embodiment, the campaign information may include a first plurality of keywords provided by an entity other than the end user of a client system. A first document associated with a first uniform resource locator (URL) may be identified. In at least one embodiment, the first document may include a first portion of original content to be displayed on the client system. Using the campaign information, specific original content of the first portion of original content may be selected to be converted to a first hyperlink having a second uniform resource locator (URL) associated therewith. In at least one embodiment, the specific original content includes a first text string matching at least one keyword from the campaign information. Markup operations may be performed on a first portion of specific original content. In at least one embodiment, the markup operations include converting the first portion of specific original content into a first hyperlink to the second URL, wherein the first hyperlink includes a first portion of marked up content. The first hyperlink may be displayed at the client system. In at least one embodiment, the display of the first hyperlink includes display of the first portion of marked up content. In at least one embodiment, when an event is detected relating to a location of a cursor at the client system being positioned over a portion of the displayed first hyperlink, a first overlay advertising impression may be automatically displayed at the client system. In at least one embodiment, the first overlay advertising impression includes advertising information comprising a second portion of content which is different from the first portion of marked up content.