.NET Framework 4.5

C# v5.0 - Visual Studio 2012
This version is a direct upgrade to .NET framework 4.0
This means that you cannot have these two versions installed side-by-side
When you install .NET 4.5 your .NET 4.0 assemblies in the \Windows\.NET Framework\V4.0.30319 are overwritten with a new set of assemblies
improvements for high DPI scenarios
new way to schedule background asynchronous worker tasks
improvements to windows forms controls resizing edit and continue for 64 bit apps async-aware debugging windows store app development
improvements to windows forms controls resizing
edit and continue for 64 bit apps
windows store app development

async

async and await keywords added
Asynchronous methods that you define by using async and await are referred to as async methods.

await

Caller Information Attributes

This allows you to obtain information about the caller to a method You can obtain the file path, line number and the member name of the caller This is useful when tracing and debugging

Larger Arrays

Support for arrays that are larger than 2 gigabyte on 64 bit platforms This feature can be enabled in the application configuration file "gcAllowVeryLargeObjects" element

Default Culture

The ability to be able to define a default culture for an application domain

Portable Class Libraries

The Portable Class Library project in Visual Studio 2012 (and later) lets you write and build managed assemblies that work on multiple .NET framework platforms You can choose to target platforms such as Windows Phone and Windows Store

WPF Ribbon Control

Allows you to implement a ribbon user interface that hosts a Quick Access Toolbar, Application Menus and Tabs.

Windows Store Apps

Windows 8.x Store apps are designed for specific form factors and leverage the power of the Windows operating system