CLR

The Common Language Runtime (CLR) is the core runtime environment of the Microsoft .NET platform. It provides a managed execution environment for code written in .NET languages and compiled to the Common Intermediate Language (CIL). The CLR handles low-level responsibilities such as memory management, type safety, exception handling, and security, allowing developers to write higher-level code without worrying about manual resource management.

Key functions include just-in-time compilation, where CIL is translated to native machine code at run time, and garbage collection, which automatically reclaims unused memory. The CLR enforces the Common Type System (CTS) to ensure language interoperability, so components written in different .NET languages can collaborate within the same process. It also supports metadata and reflection, which enable runtime discovery and interaction with types and assemblies.

Assemblies, which contain metadata and IL, are loaded by the CLR and organized in a type-safe execution environment. Cross-language interoperability is a major feature of the CLR, since multiple languages target the same runtime and can interoperate through shared types and libraries. Isolation and unloading of code are managed through mechanisms such as AssemblyLoadContext in modern runtimes, with earlier AppDomains providing a similar purpose in the .NET Framework.

Historically, the CLR was introduced as part of the .NET Framework in the early 2000s. In .NET Core and the subsequent unified .NET platform, the equivalent runtime component is CoreCLR, designed for cross-platform execution on Windows, Linux, and macOS. The CLR/ CoreCLR ecosystem enables multi-language development, performance optimizations, and evolving runtime features across the .NET family.