Starting this month, Twitter have started to place advertisements into individual users' Twitter timelines.
Marketers have previously been able to purchase ‘Promoted Tweets'; that appear at the top of searches and trending topics on Twitter.com.
This new wave of paid advertising on Twitter will target users based on the types of people and products they follow. For example, a user following other internet marketing companies or who follows users who write about internet marketing would be a target candidate for a Receptional-paid Tweet.
Twitter advertisers Virgin, Red Bull and Starbucks have already bought into this new service.