Runtime libraries overview

The .NET runtime has an expansive standard set of class libraries, known as runtime libraries, framework libraries, or the base class library (BCL). In addition, there are extensions to the runtime libraries, provided in NuGet packages.

These libraries provide implementations for many general and app-specific types, algorithms, and utility functionality.

Runtime libraries

These libraries provide the foundational types and utility functionality and are the base of all other .NET class libraries. An example is the System.String class, which provides APIs for working with strings. Another example is the serialization libraries.

Extensions to the runtime libraries

Some libraries are provided in NuGet packages rather than included in the runtime's shared framework. For example:

Conceptual content	NuGet package
Configuration	Microsoft.Extensions.Configuration
Dependency injection	Microsoft.Extensions.DependencyInjection
File globbing	Microsoft.Extensions.FileSystemGlobbing
Generic Host	Microsoft.Extensions.Hosting
HTTP	† Microsoft.Extensions.Http
Localization	Microsoft.Extensions.Localization
Logging	Microsoft.Extensions.Logging

^† For some target frameworks, including net6.0, these libraries are part of the shared framework and don't need to be installed separately.

See also

• Introduction to .NET
• Install .NET SDK or runtime
• Select the installed .NET SDK or runtime version to use
• Publish framework-dependent apps