.Net Standard is a specification that defines a set of APIs that must be supported by .NET platforms. It allows developers to write libraries that work on multiple platforms like .NET Framework, .NET Core, and Xamarin. Previously, Portable Class Libraries (PCLs) were used but they had issues like each platform decided which APIs to include and it was hard to understand compatibility. .Net Standard addresses these issues by providing a common set of APIs that all platforms must support. It uses versioning so higher versions include more APIs and libraries can target a range of versions. The .Net Standard library bridges references to existing platform libraries at build time via type forwarding. At runtime, each platform provides an implementation of the .