Wikipedia is one of the internet community's big successes
The 12-hour ban hit large numbers of people in the country because all web traffic in Qatar is routed through a single net address.
Wikipedia says pages about the US, sex and the birthday of the prophet Muhammad were vandalised.
The site is run by its users and anyone is free to alter posts in good faith.
Jimmy Wales, founder of Wikipedia, wrote: "This IP (internet protocol) number was temporarily blocked for less than 12 hours, and a block of an entire nation would go absolutely against Wikipedia policy."
In an earlier post on the Wikipedia site, it said: "Anonymous editing from this internet address is currently disabled due to a large volume of spam and vandalism that we have received from this address."
Specific users
In other cases Wikipedia bans specific users who vandalise entries to the encyclopaedia. But it was not able to do that for users in Qatar because of the way the net is configured in the country.
There is only one high speed internet service provider in the country which acts as a gateway for all users.
We wish to allow the maximum numbers of people, from everywhere
Florence Devouard, Wikimedia foundation chair
It was thought the ban was permanent but Mr Wales made clear the ban was temporary.
"In the English Wikipedia, such an action [a permanent ban] would require approval of at a minimum the English Arbitration Committee and/or me personally, and would never ever be undertaken lightly, nor without extensive attempts at direct negotiation with the ISP and/or nation in question," he wrote.
Qatar is one of the wealthiest middle eastern countries, with a population of about 630,000. It is also the home of Al-Jazeera TV, one of the most well-known Arabic TV networks.
Florence Devouard, chair of the Wikimedia foundation, told BBC News: "None of us is against any country. We come from countries all over the world. Not only the USA, not only Europe.
"We are aware some of our very good editors are sometimes blocked after a vandalism spree, this happened just a few days ago in Thailand. We unblock people as soon as possible.
"We wish to allow the maximum numbers of people, from everywhere. We just have to protect ourselves from vandals from time to time."
Wikipedia blocked editing by a proxy IP address  belonging to Internet users in the Middle Eastern kingdom of Qatar for a period of twelve hours due to persistent vandalism originating from the IP.

Only one provider of high-speed Internet access operates in Qatar, and this provider has configured its network such that all its users share the same single IP address. In most cases, a single IP address corresponds to one user or a small group of users in one building or school. Because of this single-address configuration, Wikipedia was not able to implement its usual countervandalism solution, the blocking of individual IPs or user accounts.  Wikipedia said that the action was taken after 200 repeated vandalism edits of the articles on sex, the United States, and the birthday of the prophet Muhammad.

A spokesperson for Wikipedia, said: "Qatar has not been banned from Wikipedia. Apparently Qatar basically has only one ISP, and nearly all of its traffic shows as coming from a single IP address."

Jimmy Wales, the Wikipedia founder, emphasized the temporary nature of the block, saying, "This IP number was temporarily blocked for less than 12 hours, and a block of an entire nation would go absolutely against Wikipedia policy."

At 21:26 UTC (5:26 p.m. ET) a Wikipedia admin unblocked the IP address with the reason given as: ''"This IP is the address for the entire nation of Qatar; it should not be blocked."''

Qatar only has around 219,000 Internet users, and much less of that number would actually be affected by the block.