Ecma C# and CLI Standards

In June 2006, the General Assembly of the international standardization organization Ecma approved the fourth edition of the Common Language Infrastructure (CLI) and C# specifications, as updated Ecma-334 and Ecma-335, respectively.

In July 2005, Ecma submitted the standards and TRs to ISO/IEC JTC 1 via the latter's Fast-Track process; they were adopted as standards by ISO in April 2006.

Download latest specifications

The following official Ecma documents are available for C# and CLI:

What is new in the third and fourth editions

Aside from bug fixes, major enhancements over previous editions include:



Background on previous editions

In August, 2000, Microsoft Corporation, Hewlett-Packard and Intel Corporation co-sponsored the submission of specifications for the Common Language Infrastructure (CLI) and C# programming language to the international standardization organization Ecma. As a result, Ecma formed two task groups (TG3 and TG2, respectively) within TC39, its technical committee responsible for programming languages and application development.

During the next year, the co-sponsor companies, in conjunction with other Ecma members and guests (including IBM, Fujitsu Software, Plum Hall, Monash University and ISE), refined these specifications into standards. In December, 2001, the Ecma General Assembly ratified the 1st edition of the C# and CLI standards as Ecma-334 and Ecma-335, respectively. A technical report on the CLI, Ecma TR-84, was also ratified.

In late December, 2001, Ecma submitted the standards and TR to ISO/IEC JTC 1 via the latter's Fast-Track process. The subsequent 6-month evaluation and comment period resulted in two NO votes (Japan and UK) on the draft standards, and one NO vote (Japan) on the draft TR. All comments resulting from this review were considered at a ballot resolution meeting held in October, 2002. The two NO votes on the standards were resolved, making acceptance unanimous. However, Japan did not change its NO vote on the draft TR (Japan would like to see a formatted/readable rendering of the CLI class library as part of the standard, not as a TR; this will be considered for a future edition).

The ISO/IEC standards and TR were published in April, 2003, and are known formally as ISO/IEC 23270 (C#), ISO/IEC 23271 (CLI) and ISO/IEC 23272 (CLI TR). Equivalent specifications were adopted as 2nd edition standards and TR by Ecma at its December, 2002, General Assembly.

Joining Ecma

To participate in the standardization process, contact your organization's Ecma representative. If your company does not currently participate in Ecma and wishes to do so, please contact Ecma ( directly.


The following organizations have participated in the work of Ecma TC39/TG2 and TC39/TG3 and their contributions are gratefully acknowledged: Borland, Fujitsu, Hewlett-Packard, Intel Corporation, International Business Machines, ISE, IT University Copenhagen, Microsoft Corporation, Monash University, Netscape, Novell Corporation, OpenWave, Plum Hall, Sun Microsystems, University of Canterbury New Zealand.

Many of the organizations that have participated in the TC39/TG2 and TC39/TG3 work have volunteered to mirror this site. The URLs for the mirror sites are:

This mirror is maintained by Peter Sestoft ( 2004-07-06, 2005-08-12, 2006-01-23, 2007-10-18