Updated: April 22, 2011. The Microsoft SharePoint 2010 Software Development Kit (SDK) includes documentation and code samples for Microsoft SharePoint Foundation 2010 and for Microsoft SharePoint Server 2010, which builds upon the SharePoint Foundation 2010 infrastructure. The documentation includes detailed descriptions of the technologies that SharePoint Server 2010 and SharePoint Foundation 2010 provide for developers, reference documentation for the server and client object models, and step-by-step procedures for using these technologies and object models and programming with them. This SDK also includes best practices and setup guidance to help you get started with your own custom applications that build and extend upon the SharePoint Foundation 2010 and SharePoint Server 2010 platforms.
Download details: SharePoint 2010 Reference: Software Development Kit