Microsoft has provided the ability to run Windows from a flash drive for a while, but only for those users meeting specific hardware requirements and access to Windows-To-Go (which requires an Enterprise license). I recently came across a utility, called WinToUSB, that allows any Windows user to create a bootable Windows instance on a USB flash drive.
WinToUSB can create bootable Windows sessions three different ways:
By cloning the currently running Windows instance (Windows 7 or later)
WinToUSB supports creating bootable Windows for client operating systems (Windows 7, 8, 8.1, and 10 Technical Preview) server operating systems (Windows 2008 R2, 2012, 2012 R2), and WinPE (versions 2-5).
The utility is wizard-based, allowing you to skip long, difficult command-lines and step through the creation. Though the utility will run on Windows XP and later, if you use Windows 8 or greater, you don't need an Enterprise license to create a Windows-To-Go USB drive.
You can download the free utility from here: WinToUSB