Will Windows Phone 7 or 7.5 apps run on Windows 8 tablets?

It is not okay to assume a Windows Phone 7 application will run on Windows 8 tablet. In fact, let's be clear - they will not. They will not. They will not.   Please note: this is specific to Windows Phone 7, however, not Windows Phone 8. Windows Phone 7 uses Silverlight and an abbreviated .Net framework. Metro applications are written in XAML and WinRT. These are best described as "different" and completely incompatible. Of course you can change and recompile your Windows Phone 7 application. Just be aware that the form factors are also incompatible. A small, vertically oriented phone is similar to a tablet. But don't mistake them as the same. You should put in the TLC to make your tablet app a tablet app.   You might be interested in the http://convertathon.com and this resource http://msdn.microsoft.com/en-us/library/windows/apps/hh465136.aspx

Short answer is no, current Windows Phone 7/7.5/8 apps will not run on a Windows 8 tablet. Microsoft has announced support for something they call a Universal App. This appears to address the concern that you have. These apps are intended to run on all of Microsoft's modern software platforms, including Windows 8.1, and Windows Phone 8.1.

Hi, Windows 8 Metro-style apps use XAML for their UI and is similar to the markup in Silverlight. The differenece is in the namespaces that the two use (ie where to get the resource for say a listbox), similarly c# is supported in Windows 8 so out of the box a precompiled WP7 app wouldn't run but a vendor can update the existing code to produce an app targeting Windows 8 Metro. Although not trivial it's not that hard involving a bit of copy/replace and some intellisense. I've seen someone port from WP7 to Win* in a 15 minute demo while explaing the concepts - so you'll probably see a lot of popular apps getting ported!

Windows Phone apps are specifically written to adhere to the scaling of the mobile device. It is possible to write such an application that it could be used on both platforms. But, for those that have only targeted the Windows Phone, these applications will not run well on Windows 8 at all. At best, you can install the Windows Phone emulator in order to execute any Windows Phone application on your computer. But really, you shouldn't be looking into wanting phone applications on your computer because that just doesn't make sense at all...

It would be possible if Microsoft built in support for it, but we do not know if they wish to do so and how those apps would look (snapped only or run fullscreen).