Next week in San Francisco, Microsoft will host the latest edition of its BUILD conference. A lot of exciting news should come out of this show, including information about future developments related to Windows, Windows Phone, and Xbox One. But as a developer show, BUILD is ideally suited—and well timed—for a long-rumored event: Microsoft could be purchasing Xamarin, a firm that brings Microsoft's awesome developer technologies to rival platforms like Android and iOS.

I have no opinion about whether Xamarin should accept this rumored offer. Certainly there are pros and cons. But from Microsoft's perspective, this is a no-brainer: The firm should do everything it can to bring Xamarin in-house if possible or, barring that, give it a "favored nation" status in a sweeping partnership deal.

Xamarin's importance might not be well understood outside of the relatively insular world of software development. But it goes like this: Microsoft makes the best developer tools and technologies on Earth, and even its programming languages such as C# are cleaner, better, and more efficient than what's available on platforms such as Android and iOS. Xamarin serves as a bridge between these worlds. It makes it possible to create native Android and iOS (and Mac) apps—not just Windows apps—using Microsoft's Visual Studio development environment and C# language. Developers can thus reuse code between the platforms, speeding cross-platform app development.

Microsoft, of course, has committed to being a leader in devices and services. But although many believe that this means Microsoft intends to be the only provider of those devices and services, its strategy is much more inclusive than that. And as it races to get as many of its own apps and services on rival platforms such as Android and iOS, it also wants to ease the process by which it and third parties can target all of these platforms simultaneously. That's where Xamarin comes in. It's the glue that makes cross-platform development not just possible, but viable.

Rumors about a possible Microsoft purchase of Xamarin piped up about a week ago at CRN. But Microsoft has been interested in acquiring this firm—and its cofounder, Miguel de Icaza—for years. During a party at PDC 2003 in Los Angeles, I witnessed Microsoft's Don Box (and his band, Band on the Runtime) serenade Miguel de Icaza as part of an effort to win him over to the software giant. Miguel, then at Ximian, obviously refused, but since then, he has gone on to do the work that Microsoft refused to do in the intervening decade, first on Linux and more recently for mobile platforms through Xamarin.

But times change, and Microsoft is also rumored to be announcing Office for iPad this week. Some, including my Windows Weekly cohost Mary Jo Foley, have speculated that Thursday's rumored press event for this product might also be an appropriate time to announce a purchase of or expanded partnership with Xamarin.

Whatever the timing, Microsoft buying Xamarin and folding its cross-platform capabilities into Visual Studio isn't just an excellent idea. It's necessary.