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C# language specification

5th edition, December 2017

This specification describes the form and establishes the interpretation of programs written in the C# programming language.

It describes

  • The representation of C# programs;
  • The syntax and constraints of the C# language;
  • The semantic rules for interpreting C# programs;
  • The restrictions and limits imposed by a conforming implementation of C#.

This specification does not describe

  • The mechanism by which C# programs are transformed for use by a data-processing system;
  • The mechanism by which C# applications are invoked for use by a data-processing system;
  • The mechanism by which input data are transformed for use by a C# application;
  • The mechanism by which output data are transformed after being produced by a C# application;
  • The size or complexity of a program and its data that will exceed the capacity of any specific data-processing system or the capacity of a particular processor;
  • All minimal requirements of a data-processing system that is capable of supporting a conforming implementation.

This Ecma publication has also been approved as ISO/IEC 23270:2018,
which is freely available here Link to non-Ecma site. Ecma is not responsible for the contents of the site..

Microsoft Visual C# Version Corresponding Ecma Standard Corresponding ISO/IEC Standard
V1.0 ECMA-334:2003 ISO/IEC 23270:2003
V2.0 ECMA-334:2006 ISO/IEC 23270:2006
V3.0 none none
V4.0 none none
V5.0 ECMA-334:2017 ISO/IEC 23270:2018



Download this standard


CategorySoftware engineering and interfaces

SubcategoryProgramming languages

Technical CommitteeTC39

ISO/IEC number23270


  • ECMA-334, 1st edition, December 2001Download
  • ECMA-334, 2nd edition, December 2002Download
  • ECMA-334, 3rd edition, June 2005Download
  • ECMA-334, 4th edition, June 2006Download


  • ECMA-334 1st edition Hewlett-Packard patent statementNo file available
  • ECMA-334 1st edition Microsoft patent statementNo file available
  • Patent statements' listNo file available