C# was created by Microsoft’s Anders Hejlsberg in 2000, and Ecma (ECMA-334) and ISO (ISO/IEC 23270) recognized it as an international standard in 2002 and 2003, respectively. Microsoft released C#, as well as the.NET Framework and Visual Studio, which were both closed-source. Microsoft had no open-source products at the time. Mono, a free and open-source project that provides a cross-platform compiler and runtime environment for the C# programming language, was launched four years later, in 2004. Microsoft introduced Visual Studio Code (code editor), Roslyn (compiler), and the unified.NET platform (software framework) a decade later, all of which are free, open-source, and cross-platform and support C#. Mono joined Microsoft as well, but it was not combined with.NET.

C# 10.0, which was published in 2021 in.NET 6.0, is the most recent version of the language as of 2021.