Unlike broader social networks such as Facebook and MySpace, LinkedIn hasn't raced to open its doors to third-party developers or partners. That has started to change recently, with its move this month allowing users to incorporate their Twitter accounts into LinkedIn profiles and vice versa.

Now, the professional networking site is going further, opening up its technology to third-party developers that want to extend LinkedIn to their own sites and applications. The aim is to give users easier access to accounts through their own company sites and make LinkedIn a standard part of Web-based business apps.

Think of this as LinkedIn's answer to Facebook Connect, the service that lets users log onto third-party sites using their Facebook ID. By opening up its APIs, LinkedIn hopes to make its network portable as well.

"Professionals around the world use a wide variety of applications and Web sites to get their work done, and they have spoken loud and clear that they want the ability to leverage their professional networks wherever they work," said Adam Nash, LinkedIn's vice president of search and platform products, in a blog post Monday announcing the move.

For outside sites, it means they can more easily connect with LinkedIn's affluent audience of 52 million users, more than half of whom make more than $100,000 a year. Corporate sites or Web publishers integrating LinkedIn also stand to broaden their reach and deepen engagement as users share articles or other site content within their networks.

"Essentially, LinkedIn is not just a destination anymore," said Jeremiah Owyang, a partner at digital strategy firm Altimeter Group. "You can take your network wherever you go on the Web." He added that the ability to search the LinkedIn user profile will also be possible from other sites or apps.

In response to questions posted to its developer site today, LinkedIn noted that the APIs released do not include LinkedIn features such as company profiles, job postings, events, and groups and discussions.

Some developers are already plugging into the LinkedIn platform. TweetDeck, for example, will now let users view status updates and reply to them, among other things, from within the Twitter application. And Microsoft is building LinkedIn into the 2010 version of Outlook email.

LinkedIn has also allowed some third-party apps on its own site, such as Amazon's program showing what books people in someone's network are reading. But the opening of its system is mainly geared toward pushing LinkedIn out rather than bringing developers into LinkedIn itself.

While LinkedIn has lagged in opening up its system, Owyang says the company's approach has naturally been more conservative due to its business-to-business orientation and because it's already profitable. "So, [LinkedIn] doesn't have to take big, bold steps," he said.

Last week, the company announced the launch of sponsored groups and other ad initiatives including the launch of Content Ads, a new format for companies to distribute content including white papers, blogs and RSS feeds. LinkedIn has used a combination of subscription and marketing and advertising services to build revenue.

This news story is important. I recommend that everyone read it.