The deal is the third the companies have signed over the years, but like the others, terms of this deal were not disclosed.
The announcement came at the annual Interop IT Expo and Conference going on this week in Las Vegas.
On Tuesday, Microsoft and HP announced a four-year agreement to invest as much as $180 million in building a complete corporate infrastructure for unified communications and collaboration. The deal was short on specifics, but revolved around Microsoft's SharePoint Server, Exchange Server, and OCS (Office Communications Server), combined with HP's ProCurve networking hardware and Halo Telepresence audio/visual technology.
In addition, HP plans to certify for OCS its HP dx9000 TouchSmart Business PC and specific models of its smartphones. HP also will develop IP desk phones certified for the Microsoft UC infrastructure.
The pair also said they could collaborate on new product development. That and the entire product integration project would be made easier if the two had an agreement in place to share intellectual property.
The cross-patent agreement announced today covers a broad range of products and provides each company greater access to the other's patent portfolio, Microsoft and HP said. They did not provide any other details.
Under patent law, a cross-licensing agreement gives the parties involved a license to examine patented technology that is part of commercial products. The cross-patent license allows partners to include that technology in their own products without fear of lawsuits.
In January, IEEE Spectrum rated Microsoft's patent portfolio the highest among all companies across all vertical industries. The IEEE Spectrum is a magazine put out by the Institute of Electrical and Electronics Engineers, a technology trade organization.
Microsoft's score was 3,505, while HP came in at 1,175.
Acquiring patents is seen as a way to gauge a company's ability to innovate.
Microsoft's David Kaefer, general manager of intellectual property licensing, said in a statement: "Patent cross-licensing is beneficial because it clears the way for companies to create stronger partnerships and innovate in a more open environment that is good for business, and ultimately benefits customers and end-users."