# Runtime libraries overview

The .NET runtime, which is installed on a machine for use by framework-dependent apps, 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]1http
Localization Microsoft.Extensions.Localization
Logging Microsoft.Extensions.Logging

1For some target frameworks, including net6.0, these types are part of the shared framework and don't need to be installed separately.