1. A method comprising: receiving information identifying an advertisement placement area in a document; identifying one or more characteristics of content surrounding the advertisement placement area in the document; customizing, by one or more computers, one or more advertisements based on the identified characteristics of the content surrounding the advertisement placement area in the document; and transmitting the customized advertisements for display in the advertisement placement area in the document.
2. The method of claim 1 , wherein identifying one or more characteristics of the content surrounding the advertisement placement area includes identifying font characteristics of the content surrounding the advertisement placement area.