What is .NET Framework class library?

The .NET Framework class library is a library consisting of namespaces, classes, interfaces, and datatypes included in the .NET Framework. This library is organized into namespaces that contain functionally related groups of classes. These namespaces are divided among different categories, such as data access, common types, debugging, file access, network communication, security, Windows applications, Web applications, Web services, XML data etc.

Following are some important namespaces that are defined in the .NET Framework class library:

Namespaces	Description
System	This namespace includes all common datatypes, string values, arrays, methods for data conversion, and methods related to mathematical operations.
System.Data, System.Data.Common, System.Data.OleDb, System.Data.SqlClient, System.Data.SqlTypes	These namespaces are used to access a database, perform commands on a database, and retrieve and manipulate a database.
System.IO, System.DirectoryServices, System.IO.IsolatedStorage	These namespaces are used to access, read, and write files, and retrieve file paths.
System.Diagnostics	This namespace is used to debug and trace the execution of an application.
System.Net, System.Net.Sockets	These namespaces are used to communicate over the Internet when creating peer-to-peer applications.
System.Windows.Forms, System.Windows.Forms.Design	These namespaces are used to create Windows-based applications using Windows user interface components.
System.Web, System.WebCaching, System.Web.UI, System.Web.UI.Design, System.Web.UI.WebControls, System.Web.UI.HtmlControls, System.Web.Configuration, System.Web.Hosting, System.Web.Mail, System.Web.SessionState	These namespaces are used to create ASP.NET Web applications that execute over the Internet.
System.Web.Services, System.Web.Services.Description, System.Web.Services.Configuration, System.Web.Services.Discovery, System.Web.Services.Protocols	These namespaces are used to create XML Web services and components that can be published over the Internet.
System.Security, System.Security.Permissions, System.Security.Policy, System.WebSecurity, System.Security.Cryptography	These namespaces are used for authentication, authorization, and encryption.
System.Xml, System.Xml.Schema, System.Xml.Serialization, System.Xml.XPath, System.Xml.Xsl	These namespaces are used to create and access XML files.