Similar to Google's sponsored links, initially only one 'Promoted Tweet' will appear on each search results page, increasing visibility to approximately 10 percent of Twitter users.
These will be highlighted in a similar fashion to be shown as promotional tweets when listed on the Twitter search results pages, however they will still exist as regular Tweets and organically listed to the brand's followers.
High profile brands who have already signed up to the service include Sony Pictures, Virgin America, Red Bull & Starbucks, with many more expected to follow suit.
These 'Promoted Tweets' are being rolled out into Twitter's search results from today.
This move has been noted as the "first phase" of Twitter's advvertising plans, so it certainly seems as though the feelers are out and Twitter are attempting to gain a better understanding of user experience and advertiser value that the 'Promoted Tweets' offer.
Following suit is likely to be more interaction with your indvidiual timelines with Twitter displaying relevant 'Promoted Tweets' in a way that is useful to the user.