Microsoft on Monday launched a set of lawsuits against Barnes & Noble, alleging that the bookseller's Nook eBook reader infringes on several of the software giant's patents. But the complaint has nothing to do with ebooks: Instead, Microsoft is suing because the Nook is based on Google's Android OS, which in turn is based on Linux, and Microsoft has a long-standing policy to pursue patent-licensing deals with users of both OSs, which Microsoft says make use of many of its patented technologies.

"The Android platform infringes a number of Microsoft's patents, and companies manufacturing and shipping Android devices must respect our intellectual property rights," Microsoft Corporate Vice President and Deputy General Counsel Horacio Gutierrez said. "To facilitate that, we have established an industry-wide patent-licensing program for Android device manufacturers."

Whereas HTC, which makes popular Android-based smartphones, has licensed Microsoft's technology and avoided legal action, other companies—including Barnes & Noble, Foxconn, and Inventec—have demurred. So Microsoft is taking them to court.

"We have tried for over a year to reach licensing agreements with \\[these companies\\]," Mr. Gutierrez continued. "Their refusals to take licenses leave us no choice but to bring legal action to defend our innovations and fulfill our responsibility to our customers, partners, and shareholders to safeguard the billions of dollars we invest each year to bring great software products and services to market."

Microsoft also has a similar suit pending against Motorola, which—like HTC—makes popular Android-based smartphone handsets. And Microsoft isn't alone: A lot of the mobile industry's biggest players (including Apple, HTC, Nokia, and others) are involved in a complex series of lawsuits as each tries to establish its place in this rapidly emerging market.

As for the Microsoft/B&N lawsuit, the software giant claims that the Nook eBook reader infringes on five of its patents and covers a "range of functionality  ... including natural ways of interacting with devices by tabbing through various screens to find the information they need; surfing the Web more quickly; and interacting with documents and ebooks." Microsoft says that these functions are "essential to the Android user experience."