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Framework Class Library
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<p>The Framework Class Library (FCL) is a component of Microsoft's <a href="/facts/.NET_Framework/J6QDAUhP">.NET Framework</a>, the first implementation of the <a href="/facts/Common_Language_Infrastructure/mu44u01J">Common Language Infrastructure</a> (CLI). In much the same way as <a href="/facts/Common_Language_Runtime/4Y0cUdkd">Common Language Runtime</a> (CLR) implements the CLI <a href="/facts/Virtual_Execution_System/vuQF1ntM">Virtual Execution System</a> (VES), the FCL implements the CLI foundational <a href="/facts/Standard_Libraries_(CLI)/sbGvv2nB">Standard Libraries</a>. As a CLI foundational class libraries implementation, it is a collection of reusable <a href="/facts/Class_(computer_programming)/zvzkSAtE">classes</a>, <a href="/facts/Interface_(computing)/zdfp8unT">interfaces</a>, and <a href="/facts/Value_type/0xLHHokA">value types</a>, and includes an implementation of the CLI <a href="/facts/Base_Class_Library/sbGvv2nB">Base Class Library</a> (BCL). </p><p>With Microsoft's move to <a href="/facts/.NET_Core/NhHe0l06">.NET Core</a>, the CLI foundational class libraries implementation is known as <a href="/facts/CoreFX/NhHe0l06">CoreFX</a> instead of Framework Class Library. </p>