How do I install Windows 10 to a USB Flash Drive?

I'm wondering how I can install Windows 10 to a flash drive so if I install Windows 10 to it I can just boot it up from that if I want to use it. Unfortunately I don't have a secondary computer to mess around with it, so I'm kind of restricted. In short, I don't want Windows 10 going anywhere near my hard drive. Only my flash drive.

You can't install any version of Windows to any USB attached device.  What you CAN do is partition your hard drive and install Windows 10 to the new partition.  That will give you a dual boot system where you can choose which version of Windows you want when you boot up.  You can also use virtualization.

If you would like to make one for testing purposes you can try these options:

I haven't tested these:

http://betanews.com/2014/01/13/run-windows-8-or-8-1-directly-from-a-usb-drive-on-any-computer-for-free/

http://lifehacker.com/how-to-run-a-portable-version-of-windows-from-a-usb-dri-1565509124

This one I used with windows 8 since it's similar to building your own images:

http://www.intowindows.com/how-to-run-windows-8-from-usb/

Beyond the preview builds they won't help you much because how windows is licensed it won't let you hop from computer to computer like a true windows-to-go will. Also once the preview ends you won't be able to use it anymore.

Also you won't get the performance you would get from running the OS on your computer or from a windows-to-go certified drive.

Might want to read the specifications of your usb drive before you do it.

Really needs a premium pricey usb drive to get high read and write speeds.

Good point Mike P

In addition to that, it needs to be used on a system that supports Windows 7 or later.