For an up-to-date training on how to run editathons see https://outreachdashboard.wmflabs.org/training/editathons

An edit-a-thon is an outreach event that can bring together professionals from GLAM (Galleries, Libraries, Archives & Museums) institutions and Wikipedians to improve and generate content using and linking back to institutional holdings. Below are guidelines for running a successful edit-a-thon. These guidelines are by no means comprehensive nor should they be taken as “the” single way to host an edit-a-thon.

..still under construction

Concept

Some specifics of the Editathon:

Small group (up to ~20 people)
Topical focus
Specific goals

Edit-a-thons are based on the hackathon event model.

Purpose

Editathons serve several purposes:

The social gathering introduces community members to each other
The Wikimedia editing allows people to share information with the world
The socializing and Wikipedia editing together are fun
A certain topic gets well covered, forming the base for further activities

Advantages / disadvantages

Advantages:

Good at helping build a local community among editors
Focuses attention on a particular topic
Gathers more content from female editors
...

Disadvantages:

Finding editors in a certain area interested in a certain topic can be difficult
Managing institutional expectations (what articles will be created, etc)
Not the easiest way to train new contributors, and not easy to sustain interest
...

Themes

Editathons have a theme or other specific goal and can be a way of celebrating a holiday or commemorating an event, or focusing attention on a theme or an organisation. Some possible topics include:

Geographically-based editathons for communities to improve articles on local topics
Topics connected with particular institutions, such as museums and societies.
Activist editathons for people to share unbiased information on a topic meaningful to them, such as survivors of cancer improving health articles or voters improving articles on local election issues
Topics around jubilees and national events.

Events are often directly linked to the partner institution, but do not have to be. You can look for a general theme which is still of interest to your organisation - "write about these artists" can be more productive than "write about this artwork".

Organizing the event around a theme facilitates advertising.

For example, the Mudd Library edit-a-thon was organized around the theme of "A Valentine for Princeton," as participants would be updating Princeton-related articles and the event was held the weekend after Valentine's Day. Advertising for the event capitalized on this connection to encourage participants to "show how much you love Princeton!"
Topics should follow Wikipedian principles of notability. They should not be well-developed and complete pages; either they should be redlinks, or short and flawed articles. Trying to significantly expand high-quality articles is very difficult for events. Make sure there are reliable, independent resources available for the topics you choose.

Examples

Wikipedia Loves Libraries, held during Open Access Week
Ada Lovelace events promoting women's issues, and particularly Wikipedia articles about women in science

Who does it involve?

Who are you inviting to participate in this event? If you’re holding the event at a GLAM institution, then chances are there will be GLAM practitioners who may or may not already be experienced Wikipedia users.
Invite Wikipedians from your local Wikimedia chapter to help out first-time users. A reasonable ratio of experienced-to-new users is one experienced person to three new people.

How to do it

Place, Date, Time, Length of Time

Choose a place, date and time which are convenient and appropriate for the majority of your participants. If planning to host an edit-a-thon on-site at a GLAM institution, holding the event on a Friday or a weekend day will probably be least disruptive to day-to-day operations.
Consider whether you intend participants to finish articles or simply begin them. You probably want participants to finish articles, especially since new users will probably be more inspired to continue if they have submitted a finished product after the event.
Budget at least four hours for article-writing, and consider adding more hours if participants are mostly new users, if they have to choose from a large list of topics, and if they research topics using an extensive collection of sources.
If you are inviting participants from a significant distance, the length of time for the event should reflect their effort to attend. For example, it probably would not be worth someone’s time and expense to travel three hours for a two-hour event.
If holding an edit-a-thon at a college or university where students form the majority of participants, consider that they may not want to commit more than an afternoon (four to five hours) on a volunteer, scholarly activity.
Logistical concerns of the location—hours, security, presence of salaried staff—may also constrain the length of time of the event.
Make sure there are sufficient electrical outlets if participants are bringing their laptops. Make sure visitors can access the location’s internet network. If participants are not bringing their own computers, be sure to provide sufficient access to devices on-site.
If you are planning on showing a Powerpoint presentation or other slideshow, make sure you have access to a projector and a laptop that works with it.

Social Aspects

Have participants introduce themselves at the beginning of the event. Nametags facilitate collaboration.
Create a Twitter hashtag for the event so participants can identifiably tweet about the event.
Food: depending on the time of day and budgetary considerations, having at least one meal and a snack helps people relax, connect, and refuel, making them more engaged participants. Inviting participants for a meal (and drinks, depending on the age) afterwards also fosters the collaborative spirit.
If participants are travelling for an all-day event, consider having a Backstage Pass tour at the hosting institution or of a nearby GLAM institution.

Advertising

Create a Meetup page.
Create a geonotice if you aim to attract many Wikipedia users from a broad geographic area.
For a campus setting determine the most effective channels of advertising: physical posters, online forums, institutional blogs, student newspapers, email and listserv blasts.
Ask administrative staff of the GLAM institution for permission to use administrative lists of email addresses.
Inquire if the partnering GLAM institution has any social media outlets (blog, Facebook, institutional newsletters) to which you can contribute an entry or article to advertise the event.
Consider using the event organizer's email address or another email address so that participants who are not yet Wikipedia users can RSVP.
Encourage participants to add their usernames to the Meetup page under a category of "Likely Attendees" or similar heading.

During the Event

Introduce yourself, your hosts, and have participants introduce themselves.
Depending on the experience level of participants, prepare a slideshow describing basic Wikipedian principles and editing techniques. There are resources on the bookshelf to help you with this.
Consider going through the tutorial and offering users copies of the Cheatsheet as they learn to edit Wikipedia articles.
Reiterate your goals for the day and post them on the event Meetup page.
Have participants sign up on the Meetup page if they have not already done so in order to track their contributions.
Create an Etherpad page and link to it on the Meetup page (web application available here or here or similar sites). Ask participants to write their usernames and article topics on the Etherpad so that all can see what everyone else is researching.
Update social media outlets with what participants are doing for documentation purposes.
Take pictures and post them to a Commons page for the event. Be sure to ask if all participants are comfortable with having their picture taken. Make certain it is permissible to take pictures in a GLAM institution.
Have more experienced users identify themselves so that they can answer beginners’ questions.
Welcome beginners’ input so that they feel encouraged to ask questions without fear of being put down.
Keep the mood positive and enthusiastic; you’re doing beneficial work!
Hand out stickers, buttons, or other Wiki-swag (or swag from the GLAM institution) as encouragement and as tokens of appreciation.

Outcomes

Create an Outcomes section on the event Meetup page. Tally number of articles created and updated, usernames created, images uploaded, and other notable statistics from the event.
Inquire if the partnering GLAM institution has any social media outlets (blog, Facebook, institutional newsletters) to which you can contribute an entry or article about the results of the event.
Award participants barnstars or other talk page goodies to thank them for their participation after the event.
Consider creating a case study or other deliverable for documentation purposes.
Consider creating an email list or point attendees towards existing Wikipedia and GLAM lists for more information and to keep in touch after the event.
Update this how-to with lessons from your experience!

Resources

Library Editathon Experience

Fæ was an attendee of the January 2011 and the organizer of June 2011 British Library editathons. These are his tips on running one:

Rules of thumb for running an editathon

Give yourself an 8 week time-frame for planning from the first serious discussion about the event. Though you can do things more quickly, this longer period will give time for any notices in related internet forums, discussion groups, people's blogs and even the local press to react, share information and encourage public engagement with your event.
Think carefully with the host organization as to who you would like to attract to the event and if there are any associated issues. For example the BL was not ideal for under 18s as getting a readers card is problematic. It may also be that you would prefer to attract high contribution editors rather than new Wikipedians (or vice-versa). With your target "market" clear then you can choose how and where to publicise the event.
Plan the hook for the day and let this lead your publicity. A general editathon may not be as attractive as an editathon plus an interesting presentation from a well known speaker or an editathon plus a behind-the-scenes tour or maybe not being an editathon but a "wiki-lounge" where parallel sessions might help workshop out interesting topics and help keen new contributors.
Consider whether your focus is on Wikipedia or if a focus on Wikimedia Commons or Wikinews or other major Wikimedia project might be more appropriate for an alternative interesting event. For example an event that attracts amateur photographers to share photos to illustrate related articles might do more to increase quality on Wikipedia that a pure Wikipedia article focussed event.
Think big. If you are talking to one organization, could this be part of a planned programme of events supported by a national association of museums or librarians and publicised by that association?
Avoid creating high expectation for the outcomes. It is hard to guarantee what articles will be created or improved or to what extent the public will be interested in attending, so stay flexible on the detailed content and let the attendees surprise you with their varied interests.

Other suggestions

User:Mike Peel organised the January 2011 editathon at the British Library. Here are some of his suggestions:

Make sure you have Wikimedians and curators arriving at the same time of day; curators will likely work 9-5, whereas Wikimedians generally start their days a little later. Have a fall-back plan in case one or the other group doesn't appear quite on time.
Prepare the curators in advance with a background presentation on Wikimedia, so that they know what to expect during the day (or do this right at the start of the event).
Have a list of topics that might be worked on during the event (but don't expect to work on all of them, and expect new topics to arise throughout the day)
Engage with local interest groups and include teaching them how to edit Wikipedia during the event; this then helps grow the Wikimedia community with interested researchers with available spare time (bear in mind that curators are often very busy and overworked!).
Set out the ground rules and access restrictions of the event well in advance. Can participants take photos? Can they access reference materials? If so, can they scan or photocopy those reference materials?
Combine the editathon with an event - e.g. a tour of the library, of an exhibition, etc. - to help draw in attendees.
Include an informal activity as part of the event; e.g. talking in a pub or cafe at the end of the day. This helps both sides gain understanding of the other side, and helps foster longer-term partnerships.

Sample Timeline from Mudd Library Edit-a-thon

Undead q works at Princeton University's Mudd Library and organized an edit-a-thon that was held on Saturday, 18 February. Below is the timeline reporting what was done when and suggested actions one might take in addition or instead to those listed. Please bear in mind that this edit-a-thon was conducted primarily to introduce undergraduates to editing and it was organized by an undergraduate working within a university schedule.

17 October 2011 (Four months in advance)

Determined basic schedule of day, needs for advertising, number range of participants, location, time, food plans. Determined length of time, taking into account undergraduate schedules, what we wanted to accomplish, distance participants would be traveling (i.e., making it worth their while to travel two hours for a four-hour-plus event).

18 December (Two months)

Determined publicity formats. Budgeted for posters using local student design agency. Began drafting poster design proposal. Drafted publicity blurb.

7 January (One month)

Emailed one-page blurb/invitation describing who, what, where, when, why, and reminders. Make meetup page. Make geonotice (depending on space constraints for number of participants).

7 February (11 days)

Assembled list of topics; checked to see if articles existed already. Made email list for all participants.

9 February (9 days)

Ordered Indian food for 25 people.

11 February (7 days)

Made meetup page (should have made it at the beginning). Sent reminder email.

14 February (4 days)

Finalized Powerpoint presentation describing Wikipedia principles, basic editing resources, and Princeton University Library resources relating to the edit-a-thon topic.

16 February (2 days)

Ordered pizza. Confirmed Indian food. Talked strategy with administrative staff.

17 February (1 day)

Prepared conference room; set out paper products; acquired projector, laptop, and power strips Made sure building would be open.

18 February

Picked up food. Began at 12:30 with food and mingling. Encouraged participants to add name to list on Meetup page. Showed introductory Powerpoint at 13:00. Reference archivist introduced reference room and resources therein. Edited and wrote from 13:00-16:30. Cleaned up, distributed extra food. Uploaded media to Commons. Made outcomes Etherpad and section on meetup page in evening.

22 February

Wrote blog entry for Mudd Library blog. Uploaded more photos of event.

Women at Princeton Edit-a-thon

Undead q organized another edit-a-thon in May, the Women at Princeton Edit-a-thon. The timetable was much more condensed.

19 April

Asked for University Archivist's approval to hold another edit-a-thon. Considering academic calendar and Princeton Reunions schedule, we chose a date in the middle of finals. Since we had the same number of students attend as the first event, the date did not prove a handicap.

24 April

Created publicity blurb and Wikipedia Meetup page; advertised via institutional email and Wikipedia listservs.

Between 19 April and 18 May

Developed topics and solicited archivists for topics

16 May

Ordered food.

18 May

Set up conference room with extension cords, projector, and items for food (cups, plates, et cetera).

19 May

Picked up food, set up final extension cords, set out nametags, and the event was off!

GLAM/Model projects/Edit-a-thon How-To