Twitter users will start seeing ads in their timeline over the next few weeks. The company officially announced on Thursday that a new Promoted Tweetsoption will roll out with a number of advertisers.

This is a big move for Twitter and certainly its most invasive advertising play to-date. Up until now, Promoted Tweets have only shown up in Twitter search or along user’s sidebars as a promoted Trending Topic. Now, Promoted Tweets will show up directly in the stream, with one caveat: You’ll only see ads from accounts that you already follow.

In that sense, Twitter hopes to make the ads something that users will find useful or at least be able to stomach. The company writes in a blog post: “From the start, our philosophy around advertising has been simple: We put our users first and strive to create products that enrich the Twitter experience for every Twitter user.”

The new breed of Promoted Tweets will sit “at or near” the top of a user’s timeline. However, once a user sees it for the first time, it will begin scrolling down the timeline like other tweets. Twitter also says that the tweets can be “easily dismissed from your timeline with a single click.”

Initial advertisers for the new program include a number of companies that already have significant Twitter followings, including Starbucks, JetBlue, Gatorade, Groupon, HBO and Sephora. A number of non-profits including The American Red Cross and charity: water are also participating.

The launch doesn’t come as a surprise — it’s long been suspected that Twitter would put ads in the stream. Mashable reported exclusively in June that such a product would be launched within the next two months. Now that they’re here, we’ll see if more prominent Promoted Tweets are the new DickBar or the golden monetization goose that Twitter’s been searching for.

What do you think of the new Promoted Tweets format? Let us know in the comments.