MSDN subscribers can get Windows 8.1 from MSDN Subscriber Downloads. If you're not an MSDN subscriber, you can download an evaluation version of Windows 8.1 from Evaluation Center. (Note that this version will expire, and you cannot upgrade.)
Get the headers, libraries, and tools you need to create Windows Store apps, in the language of your choice. (Includes the Windows App Certification Kit.) Learn more about the Windows SDK for Windows 8.1.
Wondering where to start?
Learn what tools you can download to get started building Windows Store apps for Windows 8.1.
Test your app before you submit it for certification and listing in the Windows Store. Learn more about the Windows App Certification Kit.
Tools to help you localize your Windows Store app with translation support, translation file management, and editor tools. Get details and additional languages.
Remote Tools for Visual Studio 2013 enables remote debugging, remote testing, and unit testing on computers that don't have Visual Studio installed. Get the Remote Tools.
A set of controls and APIs that enable apps to integrate Single Sign On (SSO) with your Microsoft account and access information from SkyDrive and Outlook.com. Learn more about the Live SDK.
Use advertising to monetize your apps while presenting a rich and engaging advertising experience to your users. Get the Microsoft Advertising SDK for Windows 8.1.
Add a scalable and secure cloud backend as well as incorporate structured storage, user authentication, and push notifications. Get Windows Azure Mobile Services.
Hundreds of samples from Microsoft to help jumpstart your project quickly. You can also download samples for a specific programming language, browse individual samples, copy code inline, and leave comments in the samples gallery.
Design your app with these essential assets, including templates, wireframes, and design guidelines. Get the design downloads.
Improve your app with services from our featured partners.