# Framework Class Library

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Standard library of Microsoft's .NET Framework

The **Framework Class Library** (**FCL**) is a component of Microsoft's [.NET Framework](/source/.NET_Framework), the first implementation of the [Common Language Infrastructure](/source/Common_Language_Infrastructure) (CLI). In much the same way as [Common Language Runtime](/source/Common_Language_Runtime) (CLR) implements the CLI [Virtual Execution System](/source/Virtual_Execution_System) (VES), the FCL implements the CLI foundational [Standard Libraries](/source/Standard_Libraries_(CLI)). As a CLI foundational class libraries implementation, it is a collection of reusable [classes](/source/Class_(computer_programming)), [interfaces](/source/Interface_(computing)), and [value types](/source/Value_type), and includes an implementation of the CLI [Base Class Library](/source/Base_Class_Library) (BCL).[1]

With Microsoft's move to [.NET Core](/source/.NET_Core), the CLI foundational class libraries implementation is known as [CoreFX](/source/CoreFX) instead of Framework Class Library.[2]

The Framework Class Library is organized into a hierarchy of namespaces, with the most commonly used functionality found in the System.* and Microsoft.* namespaces. It provides a wide range of reusable types, including collections, input/output, base data types, networking, and [XML](/source/XML) processing, which support the development of desktop, web, and server applications across the [.NET](/source/.NET) platform.[3]

## See also

- [Standard Libraries (CLI)](/source/Standard_Libraries_(CLI))

- [Base Class Library (BCL)](/source/Standard_Libraries_(CLI)#Base_Class_Library)

## References

1. **[^](#cite_ref-1)** [".NET Core vs .NET Framework: How to Pick a .NET Runtime for an Application"](https://stackify.com/net-core-vs-net-framework/). *[Stackify](/source/Stackify)*. Retrieved June 24, 2019.

1. **[^](#cite_ref-2)** [".Net CORE | Bisa Corporation"](https://www.bisacorporation.com/en/tecnology/net-core). *www.bisacorporation.com*. Retrieved December 29, 2025.

1. **[^](#cite_ref-3)** [".NET Framework Class Library (FCL)"](https://www.geeksforgeeks.org/c-sharp/net-framework-class-library-fcl/). *GeeksforGeeks*. April 30, 2019. Retrieved December 29, 2025.

[Difference Between .NET Core and .NET Framework: Head to Head Comparison](https://www.interviewbit.com/blog/net-core-vs-net-framework/)

## External links

- [.NET Framework Developer Center](http://msdn.microsoft.com/netframework/). Microsoft Developer Network (MSDN).

- [.NET Framework 3.5 namespaces](http://download.microsoft.com/download/4/a/3/4a3c7c55-84ab-4588-84a4-f96424a7d82d/NET35_Namespaces_Poster_LORES.pdf)

v t e .NET .NET strategy Libraries and frameworks Implementations .NET (Core) .NET Framework Version history .NET Compact Framework .NET Micro Framework DotGNU Mono XNA Framework Architecture Common Language Runtime (CLR) COM Interop Framework Class Library (FCL) Components ADO.NET Entity Framework ASP.NET Web Forms AJAX Core Dynamic Data MVC Razor Avalonia ClickOnce Dynamic Language Runtime Extensible Application Markup Language (XAML) Language Integrated Query (LINQ) Managed Extensibility Framework Microsoft Silverlight Microsoft XNA Parallel Extensions Windows Communication Foundation (WCF) WCF Data Services Windows Forms (WinForms) Windows Identity Foundation (WIF) Windows Presentation Foundation (WPF) Windows Workflow Foundation (WF) .NET Remoting Tools Decompilers .NET Reflector dotPeek Obfuscators Dotfuscator SmartAssembly CLR Profiler ILAsm .NET Compiler Platform Native Image Generator (NGen) XAMLPad IDEs Visual Studio Blend Express MonoDevelop SharpDevelop Xamarin Studio Organizations .NET Foundation Microsoft Xamarin Category List Commons

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Adapted from the Wikipedia article [Framework Class Library](https://en.wikipedia.org/wiki/Framework_Class_Library) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Framework_Class_Library?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.