A newly-redesigned, simple, workflow-oriented library built on the Evernote Cloud API. It's designed to drop into your app easily and make most common Evernote integrations very simple to accomplish. (And even the more complex integrations easier than they used to be.)
Setup instructions and sample snippets are all in the Getting Started guide. Have a look there next and you'll be working with Evernote in just a few minutes.
This library is the spiritual, although not syntactic, successor to to the Evernote SDK for C# 1.x. Currently, both libraries are available and supported. This one is not a "drop-in" update to the previous library -- the objects that you use to get to the traditional (EDAM) API are a little different -- and in fact, it uses the previous library for its low-level calls.
This version of the SDK is designed for Microsoft .NET 4.0 and above, for programs written in C# or VB.NET. The library is also COM-compatible, meaning it can be used for programs written in VBA (for example, inside of Microsoft Office applications).
Please check out the Evernote Developers portal page.