Evan Williams announced Monday that he will step down as Twitter's chief executive and let current chief operating officer Dick Costolo assume the role of CEO.
Williams will remain at Twitter and focus on product strategy, he wrote in a blog post.
While working on the recent recent roll-out of the "new Twitter," Williams realized that he was most satisfied working on the product side.
"Building things is my passion, and I've never been more excited or optimistic about what we have to build," he wrote.
When Williams assumed the role of CEO two years ago, Twitter had 20 employees that managed an estimated 1.25 million tweets per day. The company has since grown to 300 employees and 90 million tweets each day, he said.
"The challenges of growing an organization so quickly are numerous. Growing big is not success, in itself," Williams said. "Success to us means meeting our potential as a profitable company that can retain its culture and user focus while having a positive impact on the world. This is no small task. I frequently reflect on the type of focus that is required from everyone at Twitter to get us there."
As a result, Williams said he has asked Costolo to assume the role of CEO, while Williams will be "completely focused on product strategy."
Costolo has been in his role as Twitter COO for one year. "During his year at Twitter, he has been a critical leader in devising and executing our revenue efforts, while simultaneously and effectively making the trains run on time in the office," Williams wrote.
"I completely respect [Evan's] decision to focus on product strategy and vision. As we've all see with the new Twitter, when Ev focuses on product, something amazing can happen," Costolo said in a statement. "I'm certainly excited to be taking on this role. You couldn't ask to take a job like this at a better time - the team is incredible, we have awesome stuff in the pipeline, and we're ready to accomplish more in the next two years than we've accomplished in the last four."
The news comes the same day that Twitter experienced several glitches, officially launched its Promoted Accounts program, and unveiled its new Google TV app.