Twitter Inc. has taken a step outside its native tweet stream with news today that the company has started selling advertising on third party sites.

The initial launch will see Promoted Tweets appear on sites and apps owned by Flipboard Inc. and Yahoo! Japan, with Twitter hinting that this is just the beginning of a move into external ad sales.

The look of the third party ads will not be something akin to Google Adwords but will actually appear to be a Promoted Tweet, for example (see picture) a Nissan ad appearing on Flipboard literally appears as a tweet.

Twitter said in a blog post that the deal gives advertisers scale.

For example, let’s say Nissan is running a Promoted Tweet campaign on Twitter, but also trying to reach a similar audience on a mobile application like Flipboard. Through this new partnership, Nissan could run a Promoted Tweet campaign on Twitter, with specific creative and targeting, and simultaneously run the campaign off Twitter, with the same targeting and creative in the Flipboard app. Best of all, because Flipboard already integrates organic Tweets into the app, the Promoted Tweet will have the same look and feel that is native to the Flipboard experience.

The company continued in saying that “we think marketers will have an almost infinite capacity to create large-scale, rich and well-targeted advertising campaigns across a variety of platforms.”

It’s really a no-brainer move for Twitter. While there’s still growth opportunities in advertising on their core product, those opportunities are finite; if you’re building a strong advertising sales team why not attempt to leverage that into selling advertising on third party sites.

How far Twitter’s exploration into selling ads will go though is simply conjecture at this stage; it’s a highly competitive marketplace with more small players in it than we could ever list, and at the top of the list lies Google. If Promoted Tweets outside of Twitter itself work, and Twitter offers a competitive product in terms of price, it could well deliver solid growth opportunities for the microblogging startup going forward.

Image credit: Twitter.