The technology giant is to publish key software blueprints on its website.
It also promised not to sue open source developers for making that software available for non-commercial use.
Microsoft is being investigated by the European Commission on the grounds that limiting access to its technology could be stopping competition.
"The Commission would welcome any move towards genuine interoperability," it said.
"Nonetheless, the Commission notes that today's announcement follows at least four similar statements by Microsoft in the past on the importance of interoperability."
In January, the Commission launched two formal investigations into Microsoft for suspected abuse of its dominant market position, including one on the interoperability of its software.
The commission said it would assess whether the principles announced on Thursday were in fact "implemented in practice".
Microsoft chief executive officer Steve Ballmer said: "Our goal is to promote greater interoperability, opportunity and choice for customers and developers throughout the industry by making our products more open and by sharing even more information about our technologies."
In 2004, the commission fined Microsoft 497m euros (£375m, $735m) and forced it to offer a version of its Windows operating system without Microsoft's own media player.
The firm was also told to give competitors more information about how Windows operates, so their own software could work better with the operating system, which runs on some 90% of the world's computers.
Microsoft recently made an unsolicited bid to acquire Yahoo in a cash-and-share deal worth more than $40bn (£20.4bn), but the move was rejected.
Since then, Microsoft has stepped up its campaign to buy the firm by hiring a company that specialises in take over deals.