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.NET Framework Class Library

The .NET Framework class library is a library of classes, interfaces, and value types that provide access to system functionality. It is the foundation on which .NET Framework applications, components, and controls are built. The namespaces and namespace categories in the class library are listed in the following table and documented in detail in this reference. (Note that the table of contents lists the namespaces and categories by usage, with the most frequently used namespaces appearing first. The following list is ordered alphabetically, to provide an alternate way to navigate the class library.)

AccessibilityThe Accessibility and all of its exposed members are part of a managed wrapper for the Component Object Model (COM) accessibility interface.
Microsoft.Aspnet.SnapinThe Microsoft.Aspnet.Snapin namespace defines the types necessary for the ASP.NET management console application to interact with Microsoft Management Console (MMC). For more information, see "MMC Programmer's Guide" in the MSDN Library.
Microsoft.BuildThe Microsoft.Build namespaces contain types that provide programmatic access to, and control of, the MSBuild engine.
Microsoft.CSharpThe Microsoft.CSharp namespaces contain types that support compilation and code generation of source code written in the C# language, and types that support interoperation betwen the dynamic language runtime (DLR) and C#.
Microsoft.Data.Entity.Build.TasksThe Microsoft.Data.Entity.Build.Tasks namespace contains two MSBuild tasks that are used by the ADO.NET Entity Data Model Designer (Entity Designer).
Microsoft.JScriptThe Microsoft.JScript namespaces contain classes that support compilation and code generation using the JScript language.
Microsoft.SqlServer.ServerThe Microsoft.SqlServer.Server namespace contains classes, interfaces, and enumerations that are specific to the integration of the Microsoft .NET Framework common language runtime (CLR) into Microsoft SQL Server, and the SQL Server database engine process execution environment.
Microsoft.VisualBasicThe Microsoft.VisualBasic namespaces contain classes that support compilation and code generation using the Visual Basic language. Child namespaces contain types that provide services to the Visual Basic compiler and types that include support for the Visual Basic application model, the My namespace, lambda expressions, and code conversion.
Microsoft.VisualCThe Microsoft.VisualC namespaces contain types that support the Visual C++ compiler and types that implement the STL/CLR Library and the generic interface to the STL/CLR Library.
Microsoft.Win32The Microsoft.Win32 namespaces provide types that handle events raised by the operating system, that manipulate the system registry, and that represent file and operating system handles.
Microsoft.Windows.ThemesProvides exposure to the set of themes defined by Windows Presentation Foundation. In WPF, a theme is a set of resources, defined at the system level, which provide the default appearance for controls and other visual elements of an application. WPF themes are created using styles and include Luna, Aero, Royale, and Classic. Only the client area of a WPF application uses these themes; the appearance of the window border and buttons that form the window chrome is controlled by the Win32 theme service.
SystemThe System namespace contains fundamental classes and base classes that define commonly-used value and reference data types, events and event handlers, interfaces, attributes, and processing exceptions.
System.ActivitiesThe System.Activities namespaces contain all the classes necessary to create and work with activities in Window Workflow Foundation.
System.AddInThe System.AddIn namespaces contain types used to identify, register, activate, and control add-ins, and to allow add-ins to communicate with a host application.
System.CodeDomThe System.CodeDom namespaces contain classes that represent the elements of a source code document and that support the generation and compilation of source code in supported programming languages.
System.CollectionsThe System.Collections namespaces contain types that define various standard, specialized, and generic collection objects.
System.ComponentModelThe System.ComponentModel namespaces contain types that implement the run-time and design-time behavior of components and controls. Child namespaces support the Managed Extensibility Framework (MEF), provide attribute classes that define metadata for ASP.NET Dynamic Data controls, and contain types that let you define the design-time behavior of components and their user interfaces.
System.ConfigurationThe System.Configuration namespaces contain types for handling configuration data, such as data in machine or application configuration files. Child namespaces contain types that are used to configure an assembly, to write custom installers for components, and to support a pluggable model for adding functionality to, or removing functionality from, both client and server applications.
System.DataThe System.Data namespaces contain classes for accessing and managing data from diverse sources. The top-level namespace and a number of the child namespaces together form the ADO.NET architecture and ADO.NET data providers. For example, providers are available for SQL Server, Oracle, ODBC, and OleDB. Other child namespaces contain classes used by the ADO.NET Entity Data Model (EDM) and by WCF Data Services.
System.DeploymentThe System.Deployment namespaces contain types that support deployment of ClickOnce applications.
System.Device.LocationThe System.Device.Location namespace allows application developers to easily access the computer's location by using a single API. Location information may come from multiple providers, such as GPS, Wi-Fi triangulation, and cell phone tower triangulation. The System.Device.Location classes provide a single API to encapsulate the multiple location providers on a computer and support seamless prioritization and transitioning between them. As a result, application developers who use this API do not need to tailor applications to specific hardware configurations.
System.DiagnosticsThe System.Diagnostics namespaces contain types that enable you to interact with system processes, event logs, and performance counters. Child namespaces contain types to interact with code analysis tools, to support contracts, to extend design-time support for application monitoring and instrumentation, to log event data using the Event Tracing for Windows (ETW) tracing subsystem, to read to and write from event logs and collect performance data, and to read and write debug symbol information.
System.DirectoryServicesThe System.DirectoryServices namespaces contain types that provide access to Active Directory from managed code.
System.DrawingThe System.Drawing parent namespace contains types that support basic GDI+ graphics functionality. Child namespaces support advanced two-dimensional and vector graphics functionality, advanced imaging functionality, and print-related and typographical services. A child namespace also contains types that extend design-time user-interface logic and drawing.
System.DynamicThe System.Dynamic namespace provides classes and interfaces that support Dynamic Language Runtime.
System.EnterpriseServicesThe System.EnterpriseServices namespaces contain types that define the COM+ services architecture, which provides an infrastructure for enterprise applications. A child namespace supports Compensating Resource Manager (CRM), a COM+ service that enables non-transactional objects to be included in Microsoft Distributed Transaction Coordinator (DTC) transactions. Child namespaces are described briefly in the following table and documented in detail in this reference.
System.GlobalizationThe System.Globalization namespace contains classes that define culture-related information, including language, country/region, calendars in use, format patterns for dates, currency, and numbers, and sort order for strings. These classes are useful for writing globalized (internationalized) applications. Classes such as StringInfo and TextInfo provide advanced globalization functionalities, including surrogate support and text element processing.
System.IdentityModelThe System.IdentityModel namespaces contain types that are used to provide security and authentication in Windows Communication Foundation (WCF).
System.IOThe System.IO namespaces contain types that support input and output, including the ability to read and write data to streams either synchronously or asynchronously, to compress data in streams, to create and use isolated stores, to map files to an application's logical address space, to store multiple data objects in a single container, to communicate using anonymous or named pipes, to implement custom logging, and to handle the flow of data to and from serial ports.
System.LinqThe System.Linq namespaces contain types that support queries that use Language-Integrated Query (LINQ). This includes types that represent queries as objects in expression trees.
System.ManagementThe System.Management namespaces contain types that provide access to management information and management events about the system, devices, and applications instrumented to the Windows Management Instrumentation (WMI) infrastructure. These namespaces also contain types necessary for instrumenting applications so that they expose their management information and events through WMI to potential customers.
System.MediaThe System.Media namespace contains classes for playing sound files and accessing sounds provided by the system.
System.MessagingThe System.Messaging namespaces contain types that enable you to connect to, monitor, and administer message queues on the network and to send, receive, or peek messages. A child namespace contains classes that can be used to extend design-time support for messaging classes.
System.NetThe System.Net namespaces contain classes that provide a simple programming interface for a number of network protocols, programmatically access and update configuration settings for the System.Net namespaces, define cache policies for web resources, compose and send e-mail, represent Multipurpose Internet Mail Exchange (MIME) headers, access network traffic data and network address information, and access peer-to-peer networking functionality. Additional child namespaces provide a managed implementation of the Windows Sockets (Winsock) interface and provide access to network streams for secure communications between hosts.
System.NumericsThe System.Numerics namespace contains numeric types that complement the numeric primitives, such as Byte, Double, and Int32, that are defined by the .NET Framework.
System.PrintingThe System.Printing namespaces contain types that support printing, that provide access to the properties of print system objects and enable rapid copying of their property settings to another object of the same type, and that support the interconversion of managed System.PrintTicket objects and unmanaged GDI DEVMODE structures.
System.ReflectionThe System.Reflection namespaces contain types that provide a managed view of loaded types, methods, and fields, and that can dynamically create and invoke types. A child namespace contains types that enable a compiler or other tool to emit metadata and Microsoft intermediate language (MSIL).
System.ResourcesThe System.Resources namespaces contain types that enable developers to create, store, and manage an application's culture-specific resources.
System.RuntimeThe System.Runtime namespaces contain types that support an application's interaction with the common language runtime, and types that enable features such as application data caching, advanced exception handling, application activation within application domains, COM interop, distributed applications, serialization and deserialization, and versioning. Additional namespaces enable compiler writers to specify attributes that affect the run-time behavior of the common language runtime, define a contract for reliability between a set of code and other code that takes a dependency on it, and implement a persistence provider for Windows Communication Foundation (WCF).
System.SecurityThe System.Security namespaces contain classes that represent the .NET Framework security system and permissions. Child namespaces provide types that control access to and audit securable objects, allow authentication, provide crytographic services, control access to operations and resources based on policy, and support rights management of application-created content.
System.ServiceModelThe System.ServiceModel namespaces contain the types necessary to build Windows Communication Foundation (WCF) service and client applications.
System.ServiceProcessThe System.ServiceProcess namespaces contain types that enable you to implement, install, and control Windows service applications and extend design-time support for Windows service applications.
System.SpeechThe System.Speech namespaces contain types that support speech recognition.
System.TextThe System.Text namespaces contain types for character encoding and string manipulation. A child namespace enables you to process text using regular expressions.
System.ThreadingThe System.Threading namespaces contain types that enable multithreaded programming. A child namespace provides types that simplify the work of writing concurrent and asynchronous code.
System.TimersThe System.Timers namespace provides the Timer component, which allows you to raise an event on a specified interval.
System.TransactionsThe System.Transactions namespaces contain types that support transactions with multiple, distributed participants, multiple phase notifications, and durable enlistments. A child namespace contains types that describe the configuration options used by the System.Transactions types.
System.WebThe System.Web namespaces contain types that enable browser/server communication. Child namespaces include types that support ASP.NET forms authentication, application services, data caching on the server, ASP.NET application configuration, dynamic data, HTTP handlers, JSON serialization, incorporating AJAX functionality into ASP.NET, ASP.NET security, and web services.
System.WindowsThe System.Windows namespaces contain types used in Windows Presentation Foundation (WPF) applications, including animation clients, user interface controls, data binding, and type conversion. System.Windows.Forms and its child namespaces are used for developing Windows Forms applications.
System.WorkflowThe System.Workflow namespaces contain types used to develop applications that use Windows Workflow Foundation. These types provide design time and run-time support for rules and activities, to configure, control, host, and debug the workflow runtime engine.
System.XamlThe System.Xaml namespaces contain types that support parsing and processing the Extensible Application Markup Language (XAML).
System.XmlThe System.Xml namespaces contain types for processing XML. Child namespaces support serialization of XML documents or streams, XSD schemas, XQuery 1.0 and XPath 2.0, and LINQ to XML, which is an in-memory XML programming interface that enables easy modification of XML documents.
UIAutomationClientsideProvidersContains a single type that maps client automation providers.
XamlGeneratedNamespaceTypes in this namespace are generated by the workflow designer to aid in processing XAML defined types.