XHTML is an innovative metadata standard that blends the traditional World Wide Web markup language HTML with the less well-known markup language XML. It is currently only used in a small percentage of documents on the Web. The purpose of this paper is take a look at what sort of penetration XHTML has achieved to date, and make a preliminary effort at mapping the diffusion process of this innovation. To this end, I developed three categories of web page to examine, online shops, personal homepages, and university academic library homepages. I then proceeded to collect the URLs and document types (HTML or XHTML) of seventy-five web pages for each category. I also examined archived data to determine the approximate implementation date for those pages that had adopted XHTML. Using this data, I drew some preliminary conclusions about the state of diffusion in which XHTML is currently, as well as identifying which areas will require further study in future works.