

Twitter Chief Executive Dick Costolo, shown in July, says an initial public offering for the popular blogging platform isn't certain. Bryan Thomas for The Wall Street Journal.

Twitter, a blogging platform whose more than 200 million monthly users swap 140-character messages known as tweets, is expected to move ahead with an IPO in a year or so, people familiar with the company's deliberations have said. But the 49-year-old Twitter chief executive says going public isn't certain.

The company recently permitted investment-management firm BlackRock Inc. to buy roughly $80 million in stock from early employees, a transaction that sets Twitter's valuation at $9 billion—a lofty level for a company that eMarketer Inc. estimates will generate $545.2 million in advertising revenue this year.

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Twitter, a private company, doesn't disclose revenue or profit. On Tuesday, the company said it bought Bluefin Labs, which analyzes tweets about TV shows.

Mr. Costolo acknowledges the company is a work in progress. Among his goals: making Twitter more understandable to newcomers so the service can crack one billion users.

Interviewed recently at company headquarters in San Francisco, the former Google Inc. executive discussed spurring staff to take risks and the thinking behind Twitter's purchase of video startup Vine. Edited excerpts:

WSJ: When will Twitter go public?

Mr. Costolo: It's not necessarily inevitable. There are lots of different choices companies can make now. A couple of years ago [Twitter] had a large private financing, and you're seeing other companies do that now. I think that's great. It affords companies a lot of different ways to think about financing growth.

WSJ: Intense investor interest in tech startups, including yours, means some young companies drew particularly high valuations. How can Twitter live up to high financial expectations?

Mr. Costolo: We want Twitter to be one of the lasting, remarkable companies. Revenue and profits are the fuel that will enable us to achieve what we feel like we have to achieve, but it's always in the context of why it's important to our users and the world, and not because we have to achieve a [certain] valuation.

We knew there was a significant [revenue] opportunity here, and we went out and proved it. We're not running around thumping our chests about it, but I think we all feel vindicated. We ignored the snickering.

WSJ: Does it matter if Twitter never has as many users as YouTube or Facebook ?

Mr. Costolo: I don't think about our goals in terms of other companies. Where we want to get to is human scale, global scale. That's a billion users, not where we are today. We're the size that 99.9% of the other companies would like to be, but we believe Twitter is valuable to everybody on the planet.

WSJ: How are you trying to narrow the gap between the large number of people who have heard about Twitter, and the smaller number who try it and stick with it?

Mr. Costolo: Once you become a core user, [Twitter] is indispensable. But you have to invest, frankly, too much to get that 'aha' moment. One of the things that we're spending a great deal of time on are weekly digest emails for casual users. It's a great way for people to start realizing, 'that's amazing and I need to be checking in more frequently.'

WSJ: What are your priorities for Twitter in the next two years?

Mr. Costolo: As we grow, I worry that incrementalism will slip into our thinking. Someone will have a great idea on design, and then before they even show it to someone, they'll say, but we couldn't do that because that won't work on a phone, or that will [upset] a bunch of users. So I'm really focusing on making sure people know that they have permission to be courageous.

WSJ: Why did Twitter buy Vine, a service that lets people post six-second bursts of digital video?

Mr. Costolo: When Facebook bought Instagram [after Twitter had sought to buy it], I said we're not going do what those other guys did. We're looking for the next thing. The Vine guys showed Vine to Jack [Dorsey, Twitter's co-founder], and he called me and said, 'you gotta see this.' We all agreed that this is the next thing down the road. It's hyper-constrained publishing. It's going to force people to be creative and foster this new art form of 'how can I tell this story in six seconds?'

WSJ: Do you want Twitter to be available in China?

Mr. Costolo: We would love the people of China—and Iran—to be able to access Twitter. We are not going to make the kinds of sacrifices we might have to currently make to be unblocked in China. [Twitter, Facebook and some other companies decline to comply with China's requirement to filter out politically sensitive material.]

WSJ: How much time do you spend dealing with the legal or governmental impact of some tweets?

Mr. Costolo: As we grow internationally there is increased local scrutiny of the service. We developed a capability that enables us to abide by local law in the countries in which we operate. For example, in Germany, it is against the law to promote Nazi speech. When someone clicks on a tweet that we've had to take down via a legal request, they will get a message that says this tweet is not visible because of this request. But everyone outside that locale can still see it.

WSJ: When you were studying computer science in college, what did you picture yourself doing at this point in your career?

Mr. Costolo: I thought I was going to go be a programmer for a technology company. Those were the interviews I had in my senior year of college, and those were the job offers I got, but I decided to turn those down and go to Chicago and be an improviser.

WSJ: You personally teach a "managing at Twitter" course to each new manager. Why?

Mr. Costolo: I have to make sure people are managing the way I want them to manage, and consistently across the company. I worked on [course planning] for five or six months and eventually built it into this three-segment course that I teach over two days. Those are great teaching moments when the CEO is standing in front of you and saying, 'here's a great example of someplace I screwed this up.'

Write to Shira Ovide at