Although some bloggers have (or have achieved) prominence and expertise that makes them as influential in politics and other areas as established journalists, reviewers, and critics (some of which maintain blogs themselves), many bloggers reach relatively few readers and discuss matters of largely personal interest. Blogs are also used by politicians, businesses, and others to keep voters, customers, and the like informed on matters of common interest; they can function as a significant alternative to television, newspapers, and other mainstream media, especially in nations where the media are controlled or censored by the government. Bloggers have at times broken important news stories or marshalled public opinion on a matter of public interest.

Online journals first appeared in the early 1990s. The development in the late 1990s of software that made updating an online journal easier and the subsequent rise of websites that specialized in hosting blogs spurred the rapid growth of blogging in the first years of the 21st cent., and by the mid-2000s there were millions of blogs on the Internet.