This paper analyses online users’ debates about the generic classification and ancestry of “blogs” and “Internet diaries,” looking in particular at users’ defensive definitions and meta-generic commentary that would distinguish the blog from the diary. It is argued that these directives draw on traditional generic stereotypes, reproduced from print culture, that associate the diary with the narcissistic, feminine, and amateur, qualities apparently antithetical to self-styled “bloggers.” Since actual practice does not necessarily support a tenable distinction between blogs and diaries, it is suggested that such genre claims arise from and protect particular communities’ ideals about the World Wide Web—and therefore its forms of communication—as novel. These often-heated commentaries offer opportunities to explore how communities understand and invest in genre in an evolving situation. A blog is not a diary. A diary is where you store private information and self reflection about your life, snapshotted feelings, etc. A blog is publicly there for anyone to see….A blog is a living autobiography… –Austin (2006 19 Oct.) Weblog, n. A frequently updated web site consisting of personal observations, excerpts from other sources, etc., typically run by a single person, and usually with hyperlinks to other sites; an online journal or diary. –Oxford English Dictionary (2003) Defining “blog” is a fool’s errand. –Jeff Jarvis (2005 27 Aug.).