This article is about the type of website. For the record of web server activity, see server log.
A weblog, or simply a blog, is a website which contains periodic, reverse chronologically ordered posts on a common webpage. Such a web site would typically be accessible to any Internet user. Part of the reason "blog" was coined and commonly accepted into use is the fact that in saying "blog", confusion with server log is avoided. Individual posts (which taken together are the blog or weblog) either share a particular theme, or a single or small group of authors.
The totality of weblogs or blog-related webs is usually called the blogosphere. The format of weblogs varies, from simple bullet lists of hyperlinks, to article summaries with user-provided comments and ratings. Individual weblog entries are almost always date and time-stamped, with the newest post at the top of the page. Because links are so important to weblogs, most blogs have a way of archiving older entries and generating a static address for individual entries; this static link is referred to as a permalink. The latest headlines, with hyperlinks and summaries, are offered in weblogs in the RSSXML-format, to be read with a RSS feedreader.
Before blogging became popular, digital communities took many forms, including Usenet, email lists and bulletin boards. In the 1990's electronic form software, such as WebX, created running conversations with threads. Many of the terms from weblogging were created in these earlier media. For example troll, a person who disrupts a discussion, dates back to Usenet. The word "thread" from email lists and usenet as well. The verb "to post" from electronic bulletin boards.
Blogging combined the personal web page, with tools to make linking to other pages easier, specifically blogrolls and trackbacks, as well as comments. This way, instead of a few people in control of threads on a forum, or anyone able to start threads on a list, there was a moderating effect that was the personality of the weblogs owner.
"Weblogs are often-updated sites that point to articles elsewhere on the web, often with comments, and to on-site articles. A weblog is kind of a continual tour, with a human guide [whom] you get to know. There are many guides to choose from, each develops an audience, and there's also comraderie and politics between the people who run weblogs, they point to each other, in all kinds of structures, graphs, loops, etc." -- Dave Winer, 
The shorter version, "blog," was coined by Peter Merholz who in April or May of 1999 broke the word weblog into the phrase "wee' blog" in the sidebar of his weblog . This was interpreted as a short form of the noun  and also as a verb, to blog, meaning "to edit one's weblog or a post to one's weblog". Usage spread during 1999 and the word was popularized by Pyra's creation of their weblog service Blogger. As of March 2003, the Oxford English Dictionary included the terms weblog, weblogging and weblogger in their dictionary. 
One of the pioneers of the tools that make blogging more than merely websites that scroll is Dave Winer of the Berkman Center at Harvard University. One of his most important contributions was the creation of servers which weblogs would "ping" to show that they had updated. This made it possible for blogs to easy "trackback" other blogs that referenced a particular story, a key feature of blogging.
In early 2002, blogs began to spring up to support the invasion of Iraq, these "war bloggers" were primarily from the right end of the spectrum, and included Instapundit and Little Green Footballs. The first "blog" driven controversy is probably associated with the fall of Trent Lott, where bloggers found quotes from his previous speeches which were taken to be racist, and "kept the story alive" in the press.
By this point blogging is enough of a phenomenon that howto manuals had begun to appear, primarily focusing on using the tools, or creating content. But the importance of a blog as a way of building an electronic community had also been written on, as had the potential for blogs as a means of publicizing other projects.
Through 2003, weblogs gained increasing notice and coverage for their role in breaking, shaping or spinning news stories. The triggering event was the sudden emergence of an opposition to the Iraq war which was not rooted in the traditional anti-war left. The blogs which gathered news on Iraq, both left and right, exploded in popularity, and Forbes magazine covered the phenomenon. The use of blogs by political candidates, particularly Howard Dean and Wesley Clark cemented their role as a news source, while the increasing number of experts who blogged, including Daniel Drezner and J. Bradford DeLong gave the blog world a cachet among regular journalists.
The Iraq War was the first "blog war" in another way - bloggers in Baghdad gained wider readership, and one published a book of his blog. Reading the thoughts of people who were "on the spot" provided a counterpoint, if not a counterweight, to official news sources. Blogs were often used to draw attention to obscure news sources, for example posting links to the traffic cameras in Madrid as a huge anti-terrorism demonstration filled the streets in the wake of the M11 attack. Bloggers would often provide nearly instant commentary on televised events, which became a secondary meaning of the word "blogging", such as "I am blogging Rice's testimony", i.e. "I am writing my reactions to Rice's testimony as I watch it."
In 2004, the role of blogs became increasingly mainstream, as political consultants, news services and candidates began using theme as tools for outreach and opinion formation. Minnesota Public Radio broad cast a program by Christopher Lydon and Matt Stoller called "The Blogging of the President", which covered the transformation in politics that blogging seemed to presage. The Columbia Journalism Review began regular coverage of blogs and blogging. Anthologies of blog pieces began to reach print, and blogging personalities began appearing on radio and television.
Many more advanced bloggers prefer to generate their blogs by using server-side software tools such as Movable Type, WordPress, and Manila to publish on their own Web site or a third party site, or to host a group of blogs for a company or school. Such programs provide greater flexibility and power, but require more knowledge. If they provide a Web interface for editing, server-based systems may reduce the ease of creating and editing text for travellers, some of whom like to produce their travelblogs from Internet cafes as they travel around the globe.
Many blogging tools have also been developed to improve the blogging experience, with commonly used ones providing blogrolls and feedback comment systems. Well known examples of these are blogrolling and the commenting system HaloScan. Tools such as Ecto and w.bloggar allow users to maintain their Web hosted blog without the need to be online while composing or editing posts. Enhancements to weblog technology continue to be developed, such as the TrackBack feature introduced by Movable Type in 2002 and subsequently adopted by other software companies (e.g., Userland) to enable automatic notification between websites of related content -- such as a post on a particular topic or one which responds to a post on another blog .
Blogs with features such as TrackBack are credited with complicating search engine page ranking techniques  and confusing (perhaps deliberately gaming) search engines that try to establish context.
Web hosting companies and online publications also provide blog creation tools, such as Salon, Tripod, and America Online, which calls its subscriber blogs "journals."
Often, the word blog is used to describe an online diary or journal, such as LiveJournal. The weblog format of an online diary makes it possible for users without much experience to create, format, and post entries with ease. People write their day-to-day experiences, complaints, poems, prose, illicit thoughts and more, often allowing others to contribute, fulfilling to a certain extent Tim Berners-Lee's original view of the World Wide Web as a collaborative medium. In 2001, mainstream awareness of online diaries began to increase dramatically.
Online diaries are integrated into the daily lives of many teenagers and college students, with communications between friends playing out over their blogs. Even fights may be posted in the diaries, with not-so-veiled insults of each other easily readable by all their friends, enemies, and complete strangers. Online diaries may also be a bane to job seekers, if their diaries are discovered by potential employers.
Political blogs attracted attention because of their use by two insurgent political candidates in 2003: Howard Dean and Wesley Clark. Both gained political buzz on the internet, and particularly among bloggers, before they were taken seriously by the establishment media as candidates. Joe Trippi, Dean's campaign manager, made the internet a particular focus of the campaign. Both candidates stumbled in the end, but were, at one time or another, thought of as front runners for the Democratic Nomination.
BlogPulse - Full-text search engine for blog postings. Also analyzes Top Links, Key People, Key Phrases, and produces BlogBites every day. Showcases trend graphs from the blogosphere. Allows you to create your own trend graphs.
Blogshares - A fantasy stock market where weblogs are the companies. Players invest fictional dollars on shares in blogs. Blogs are valued by their incoming links and add value to other blogs by linking to them. Prices can go up or down based on trading and the underlying value of the blog.
Weblogs.com - a list of weblogs updated in the last three hours
Amy Weik has Short Fingernails About automoblies, cycling, traveling, music, crazy hair, project management, vegetarianism, and Formula One. http://www.shortfingernails.com
Ambival.net Random musings, updated far too often. http://ambival.net/
Array Daily links in reference to art and applied digital technology. http://array.editthispage.com
Also not Found in Nature Weblog maintained by Owen Boswarva, with an emphasis on hard news, public policy issues, and developments in science and technology. http://www.hullocentral.demon.co.uk/site/anfin.htm
Arbitrary Inspiration Just a bloggin' chick. No promises she won't be boring, or stupid, but its her. http://www-unix.oit.umass.edu/~astanton/index.html
Angel-Kissez This site has a weblog, live webcam, and pictures. http://www.angel-kissez.com
Andrea's Weblog Weblog and personal site about reading, science, travel, education and this 'n that. Travel journals with lots of photos included. http://andrea.editthispage.com/
Attu Sees All Everything Attu sees and finds interesting or just fun. http://attu.blogspot.com
aka Cooties An under-employed web designer from Hamilton, Ontario. Daily updates, some of which are actually true. http://blog.akacooties.com/
Ant's Eye View The online journal of anthill communities. Communities of purpose where people work together, not because they're from the same background, but because they share a common goal that all would like to see realized. http://www.antseyeview.com/
Annie's Web Weblog of links to off-beat news, sites and games. http://surf-gal.tripod.com/
Amidst a Tangled Web Sort of a semi-blog of occurrences and opinion on things. Activities/ interests include programming, Linux, web design, philosophy, humor, motorcycles and life. http://dan.hersam.com/
As Above The Weblog of Kevan Davis; a variety of thoughts, rants and outside influences. http://kevan.org/blog
Andersja's Blog Author writes on various topics of interest. http://www.jacobsen.no/anders/
Amnesiac Productions Journal of one man's ongoing mission to make a movie. http://www.amnesiacproductions.com
The Audi Olympics A daily journal of life as a copywriter, editor, corporate commentator and tennis player. http://audiolympics.blogspot.com
Androgynous Mind Personal, interactive website, weblog, photolog, journal, and more, of a twenty-something SKA fanatic gay gal from Europe, living in the States. http://www.AndrogynousMind.com
An Artist's Journal Online journal of Carol Ott, graphic artist and painter. http://www.csott.com
Amber Weblog about great music, books, movies, art, graphic design and life. http://ambo.weblogs.com
Attic Blog for the post-modem literati. Steven is lost among the dusty tomes in his attic searching for the Philosoper's Stone. http://attic.blogspot.com
Anglepoised Concentrates on music, film, food, literature, technology and tequila. More fun than a barrel of dead monkeys. http://www.anglepoised.com/
The Art of Peace Weblog about politics and how the blogosphere can improve it. http://www.theartofpeace.blogspot.com
Anubis Treeli's personal weblog about daily life, including college, sorority, and relationship issues as they are encountered. http://www.plusmoutarde.com
Albert Youn Read his thoughts. http://www.xanga.com/home.aspx?user=albertyoun
Afterthoughts New York City writer and poet Jade Walker. Come to this frequently altered page for her commentary on life, love and intriguing Internet finds. http://www.jadedwritings.com/pages/after.html
Ahoyhoy.org A web log with daily posts and links about current events and other interesting topics. Users are able to reply to posts with their own comments. http://ahoyhoy.org
Ariel Pay It 4ward Ariel's blog, about paying it forward, the little mermaid, the Isle of man and her life. http://www.arielpayit4ward.com
Avocados: Musical Musings An aspiring musician looks at the humorous aspects of music, school, and life in general. Includes tips on how to practise, list of things to do before a performance, and great links. http://symphonicprose.blogspot.com
Alt Text Personal narrative on a variety of topics, current issues and events. Creative" experiments and more web fun. http://www.alttext.com
Ataxia The interbox tendency of Matthew Mittelstadt. http://www.ataxia.net/
Adampsyche A blog about current events, hockey, my son Jasper, hockey, technology, and a little more hockey. http://www.adampsyche.com
Anvari Ahmad Anvari, a compuworm from Berkeley writes about technology news, fun, business and economy every day. http://www.anvari.org/log
All This ChittahChattah A Canuck in Silicon Valley entertains you with the fascinating minutiae of life. http://chittahchattah.blogspot.com
Ace Davis virtual virtuosity. What's on the mind and off the chest. http://acedavis.blogspot.com/
Arcana.co.nz 20 years old, PostmanPat lives in an underground cave located under the city of Wellington, New Zealand. http://www.arcana.co.nz
An Artist's Life A weblog on current affairs and culture in Portland, the State of Oregon, and the Pacific Northwest region. http://abcraghead.photo-addicts.com/
Amanda Peterson Amanda Peterson pictures included in a blog. http://www.tjmulligans.blogspot.com
About a Boy Marius blogs things he cares about, often travel and music. http://home.no.net/factotum
Absolute Piffle Run by Richard Gillmann. Each post contains links and commentary with the occasional diary-type entry. Also contains links to other weblogs and online journals. http://www.nwfolk.com/piffle.html
Analog2Digital A newly 'bloggerized incarnation of Bill Pena's primer to everything : links to hyperfiction, geekology, politics and whatever other weblogs link to. http://www.pena-smith.com/bill/blogger.html
Aderemi's Notebook A Nigerian's essential guide to London with a dash of politics. http://www16.brinkster.com/soulretro/
Argos Jason Eliaser's (aka Iason) hideously boring blog. Contents: Why LexisNexis sucks, law school application process and progress, comics and other nifty media, and other self-indulgent crap. http://blargos.blogspot.com
Asciii's weBlog Just his ongoing thoughts and art. Photoblog. http://asciiiblog.tk
Abbadabbado.com Web design, filler: info about Abbey, a blog, pictures, just a bunch of random stuff. http://www.abbadabbado.com
Azores Adventure The story of the 2003 AZAB ocean race. Well, the AB (and back) part anyway. http://andback.blogspot.com
Atmaspheric Endeavors A multitasked stream of consciousness focused on: technology; multimedia; home theater; blogs and life. http://www.atmasphere.net/mt/
Alyshajane Lives in NSW Australia. Studying towards a Bachelor of Technology. http://www.alyshajane.com/
Araes' Mojo roleplaying, games, music, and anything of personal interest. http://www.uidaho.edu/~putn4403/
Aigoo-Chamna Net Aigoo Chamna means "good grief" in Korean. http://aigoo-chamna.net/
Autodidact Commentary on technopolitical issues and discussion of personal activities. http://adytum.blogspot.com
Angel Eyes This is a blog of Katie. Pictures of FFX and Harry Potter are also here. List of cliques. http://www.freewebs.com/prudentia/main.html
Annia.network Working with Adobe Illustrator and writes a very interesting weblog with cute illustrations. http://imgs.creamspace.net
Argentimes Selected news and information from Argentina. http://argentimes.antville.org
AlexHansford.com London-based weblog of a twenty-something bloke as he navigates London, life and the Internet. http://www.alexhansford.com
Abraxas Notes from London: comment on the web, news, music and life in general. http://www.abraxasblog.co.uk/
Anti-com.com This ain't your grandma's news source. http://www.anti-com.com
Acts of Volition Written by Steven Garrity, Rob Fletcher and Matthew Dorrell. http://actsofvolition.com/
Adam Gerstein Net Weblog of Adam Gerstein: designer, part time programmer, father. http://adam.gerstein.net
Anchulis The personal website and daily journal of Rachael Halloran. http://www.anchulis.com
Apophatic World Lachrymology, life, love, sex, and anything else in between. http://www.innercatharsis.blogspot.com/
Anodyne Commentary about the safest and most creative use of mind-altering drugs, and reports of the terrible costs of the war against drug users. Blurbs for art, music and writing of interest to the psychotropic community. http://www.involution.org/anodyne/
Asterisk Art, new media, design, user interface, graphic design, music, personal, Web, information architecture, motion design. http://www.7nights.com/asterisk/
AnalogousMember We all share a common thread, 'cept it looks a little different depending on who you are. http://www.analogousmember.com
Aglet by Jim Service Self-described as "News 'n' stuff from the end of a shoe string", this weblog exhibits personal news, ramblings and humour items from somewhere in Mississauga. http://www.hubbo.com
Aquarionics Personal website and weblog of Aquarion. http://www.aquarionics.com
The Aardvark Speaks Random thoughts and ramblings on libraries, politics, food, the Internet and personal stuff by Horst Prillinger, a librarian from Vienna, Austria. http://mailbox.univie.ac.at/~prillih3/blog/
Amit Kothari Covering technology, poetry, beat news and links. http://www.amitkoth.com/weblog/movabletype/myfiles/
Angryanna Anganna's thoughts and rants on her rather strange world. http://angryanna.blogspot.com
Aemilius' Blog Spot Thoughts (with apologies to Pascal) of a crabby, cranky, crotchety, cantankerous, crusty, cynical, cross, curmudgeonly, but couth and convivial old codger and compulsive communicator. http://aemilius.blogspot.com/
Araumi's Blog A place for (Araumi/ Fern) to write down thoughts/ ideas and anything else. http://araumi.blogspot.com
Aaron's Blog 'n Site This is just Aaron's random musings. Don't worry, he likes you and thinks you are a nice person. http://www.aaronwood.net/
Ay! Cristina! An Argentinian woman's trawlings of the web. http://www.livejournal.com/users/cristna/
The Apartment Women A band who are are roommates. whatever they want to be. http://www.theapartmentwomen.com
Anarchy in Motion News, oberservations, pictures and weird experiments. http://metal-militia.microphallus.com/
Aging Young Rebel Latitudinarian pansophist with eclectic ever-evolving tastes and a predilection for all things out of the ordinary. A die-hard cynic (and proud of it). http://www.backwash.com/content.php?id=87
Andreas Hochsteger A personal weblog which covers topics like XML, Java, Semantic Web, RDF, new technology. http://highstick.blogspot.com/
Andymatic Caustic and witty. Hoosier-born creativity coach and web-head in Chicago, Illinois. http://www.andymatic.com/
Andrew Phelps Thoughts and photos from San Diego. A journalist with a computer-nerd identity crisis. http://www.andrewphelps.com
A Photoblog Chris M.'s photoblog. http://www.aphotolog.com
Alden Bates' Journal The life of a computer programmer from New Zealand. Sometime it's even interesting. http://www.livejournal.com/users/abates/
Allnada It's a blog about nothing. http://www.allnada.com
Airsoft Gun News at Air Soft Alley A place for all things airsoft. Reviews, airsoft related news, tips, tricks, and an airsoft field guide for the entire world. http://www.airsoftalley.com/
Archibald Jude The Sausage King of Tiburon. Every newborn monkey ought to have his own domain. http://www.archibaldjude.com
Amazondotcom The unofficial weblog covering Amazon.com, the juggernaut of e-commerce. If you're hooked on shopping online, read this blog. (Note: We are not associated with Amazon.com in any way, but we do spend lots of cash there.) http://amazondotcom.blogspot.com/
Amarogue Visit interesting sites on the net. Enjoy links to articles of various topics. http://www.amarogue.com
Anti-Pedophile Parody and satire attacking the Catholic Church's handling of the pedophile priest crisis. http://antipedophile.blogspot.com
Aisha Elderwyn This is Aisha's personal journal in which you can read about, reply and share her life. http://aisha.livejournal.com
AlanBarber.Org Blog about topics including movies, tv, music, computers, video games, and politics. http://www.alanbarber.org
Appleman The fruit of possiblity. A site dedicated to waking people up. http://www.appleman.blogspot.com
Autoworld Selected news, links & articles relating to the automobile industry. http://autoworld.tblog.com/
Abstract Thoughts There is nothing good or bad, but thinking makes it so. Thoughts of an incessant blogger on technology, science, art, religion, spiritualism, humor and news. http://chandru.kaaninilam.com/blogs/abstractthoughts/
Anna Banana A blond blogger trying to find my way through the maze. http://www.anna-banana.net/mt/