Oct 5, 2010 08:15 GMT  ·  By

Twitter announced an executive shift at the very top as cofounder Evan Williams steps down as CEO to be replaced by current COO Dick Costolo.

Williams will focus on product strategy and vision while Costolo is said to be working on driving up revenue.

"I am most satisfied while pushing product direction. Building things is my passion, and I’ve never been more excited or optimistic about what we have to build," former CEO Evan Williams wrote.

"This is why I have decided to ask our COO, Dick Costolo, to become Twitter’s CEO. Starting today, I’ll be completely focused on product strategy," he announced.

"Given Dick’s track record as a three-time successful CEO, I’m confident we can make this a smooth transition," he added.

The move has been generally seen as a very smart one. Twitter is at a point when it needs to focus on bringing in more money.

In the two years Williams has been CEO, the service grew from 3 million registered users to 165 million. The company itself went from 20 employees to 300. Finally, the tweet traffic exploded, going from 1.25 million tweets per day to 90 million.

Twitter is still growing, but things have stabilized. With Twitter having no intention to sell, it's time to focus on revenue. This is were Costolo comes in.

He is largely responsible for the rather interesting advertising products Twitter has been pushing out lately, Promoted Tweets, Promoted Trends and so on.

Williams on the other hand is the man behind the New Twitter which is now available to a large percentage of users and has been met almost with universal praise. Clearly he can build a great product and that's what he's going to do from now on.

Other than Costolo taking over as CEO, there are no other changes in Twitter management. The COO position will not be filled by anyone else and Jason Goldman, VP of Product will continue to work with Williams.