Iran's controversial presidential election was the top Twitter topic in 2009, the wildly popular microblogging service said on Tuesday.
"Among all the keywords, hashtags, and phrases that proliferated throughout the year, one topic surfaced repeatedly," Twitter said in a blog post.
"Twitter users found the Iranian elections the most engaging topic of the year."
The San Francisco-based sensation that lets people broadcast news in short text messages using computers or mobile telephones was a primary communications tool by protestors in Iran angered by the results of their presidential election.
Late king of pop Michael Jackson was the most tweeted about person, while "Harry Potter" was the film that caused the most Twitter buzz, according to the Internet firm.
Google Wave, billed as the next step in the evolution of email, was the most tweeted about technology, according to Twitter.
With the Wave, email or instant messages blossom into shared online arenas where anyone in the exchange can edit documents, add digital content, or comment at any time.