| Accessibility | The Accessibility namespace is a part of the managed wrapper for the COM accessibility interface. |
| Microsoft.Activities | The Microsoft.Activities namespace provides support for Windows Workflow Foundation applications. |
| Microsoft.CSharp | The Microsoft.CSharp namespace has support for compilation and code generation for the C# source code. |
| Microsoft.JScript | The Microsoft.JScript namespace has support for compilation and code generation for the JScript source code. |
| Microsoft.VisualBasic | The Microsoft.VisualBasic namespace has support for compilation and code generation for the VisualBasic source code. |
| System | The System namespace has base classes for definition of interfaces, data types, events, event handlers, attributes, processing exceptions etc. |
| System.Activities | The System.Activities namespace handles the creation and working with activities in the Window Workflow Foundation using various classes. |
| System.Collections | The System.Collections namespace has multiple standard, specialized, and generic collection objects that are defined using various types. |
| System.Configuration | The System.Configuration namespace handles configuration data using various types. This may include data in machine or application configuration files. |
| System.Data | The System.Data namespace accesses and manages data from various sources using different classes. |
| System.Drawing | The System.Drawing namespace handles GDI+ basic graphics functionality. Various child namespaces also handle vector graphics functionality, advanced imaging functionality, etc. |
| System.Globalization | The System.Globalization namespace handles language, country, calendars used, format patterns for dates, etc. using various classes. |
| System.IO | The System.IO namespaces support IO like data read/write into streams, data compression, communicate using named pipes etc. using various types. |
| System.Linq | The System.Linq namespace supports Language-Integrated Query (LINQ) using various types. |
| System.Media | The System.Media namespace handles sound files and accessing the sounds provided by the system using various classes. |
| System.Net | The System.Net namespace provides an interface for network protocols, cache policies for web resources, composing and sending e-mail etc. using various classes. |
| System.Reflection | The System.Reflection namespace gives a managed view of loaded methods, types, fields, etc. It can also create and invoke types dynamically. |
| System.Security | The System.Security namespace has the .NET security system and permissions. Child namespaces provide authentication, cryptographic services etc. |
| System.Threading | The System.Threading namespace allows multithreaded programming using various types. |
| XamlGeneratedNamespace | The XamlGeneratedNamespace has compiler-generated types that are not used directly from the code. |