The International Committee for Weights and Measures (ICWM) (French: Comité international des poids et mesures (CIPM)) consists of eighteen persons, each of a different nationality, from Member States of the Metre Convention appointed by the General Conference on Weights and Measures (CGPM) whose principal task is to promote worldwide uniformity in units of measurement by taking direct action or by submitting proposals to the CGPM.
The ICWM meets every year (since 2011 in two sessions per year) at the International Bureau of Weights and Measures (BIPM) where, among other matters, it discusses reports presented to it by its Consultative Committees. Reports of the meetings of the CGPM, the ICWM, and all the Consultative Committees, are published by the BIPM.
In 1999 the ICWM has established the ICWM Arrangement de reconnaissance mutuelle (Mutual Recognition Arrangement, MRA) which serves as the framework for the mutual acceptance of national measurement standards and for recognition of the validity of calibration and measurement certificates issued by national metrology institutes.
The ICWM has set up a number of consultative committees (CC) to assist it in its work. These committees are under the authority of the ICWM. The president of each committee, who is expected to take the chair at CC meetings, is usually a member of the ICWM. Apart from the CCU, membership of a CC is open to National Metrology Institutes (NMIs) of Member States that are recognized internationally as most expert in the field. NMIs from Member States that are active in the field, but lack the expertise to become Members, are able to attend CC meetings as observers. 
These committees are:
- CCAUV: Consultative Committee for Acoustics, Ultrasound and Vibration
- CCEM: Consultative Committee for Electricity and Magnetism
- CCL: Consultative Committee for Length
- CCM: Consultative Committee for Mass and Related Quantities
- CCPR: Consultative Committee for Photometry and Radiometry
- CCQM: Consultative Committee for Amount of Substance - Metrology in Chemistry and Biology
- CCRI: Consultative Committee for Ionizing Radiation
- CCT: Consultative Committee for Thermometry
- CCTF: Consultative Committee for Time and Frequency
- CCU: Consultative Committee for Units
The CCRI has three separate sub-committees, each looking at different parts of the electromagnetic spectrum.
The CCU's role is to advise on matters related to the development of the SI and the preparation of the SI brochure. Unlike other CC's, its membership is made up of nominees from other prominent national and international bodies such as International Organization for Standardization (ISO), National Institute of Standards and Technology (NIST), National Physical Laboratory (NPL), International Astronomical Union (IAU), International Union of Pure and Applied Chemistry (IUPAC) and International Union of Pure and Applied Physics (IUPAP).[Note 1]
Official reports of the ICWM include:
- Reports of ICWM meetings (Procès-Verbaux) (ICWM Minutes)
- Annual Report to Governments on the financial and administrative situation of the BIPM
- Notification of the contributive parts of the Contracting States
- Convocation to meetings of the CGPM
- Report of the President of the ICWM to the CGPM
From time to time the ICWM has been charged by the CGPM to undertake major investigations related to activities affecting the CGPM or the BIPM. Reports produced include:
The Blevin Report
The Blevin Report, published in 1998, examined the state of worldwide metrology. The report originated from a resolution passed at the 20th CGPM (October 1995) which committed the ICWM to
to study and report on the long-term national and international needs relating to metrology, the appropriate international collaborations and the unique role of the BIPM to meet these needs, and the financial and other commitments that will be required from the Member States in the coming decades.
The report identified, amongst other things, a need for closer cooperation between the BIPM and other organisations such as International Organization of Legal Metrology (OIML) and International Laboratory Accreditation Cooperation (ILAC) with clearly defined boundaries and interfaces between the organisations. Another major finding was the need for cooperation between accreditation laboratories and the need to involve developing countries in the world of metrology.
The Kaarls Report
The Kaarls Report published in 2003 examined the role of the BIPM in the evolving needs for metrology in trade, industry and society.
The ICWM has responsibility for commissioning the SI brochure, which is the formal definition of the International system of units. The brochure is produced by the CCU in conjunction with a number of other international organisations. Initially the brochure was only in French – the official language of the metre convention, but recent versions have been published simultaneously in both English and French, with the French text being the official text. The 6th edition was published in 1991, the 7th edition was published in 1998, and the 8th in 2006.
- History of the metre
- International Bureau of Weights and Measures (BIPM)
- Institute for Reference Materials and Measurements (IRMM)
- National Institute of Standards and Technology (NIST)
- Joint Committee for Traceability in Laboratory Medicine
- Seconds pendulum
- This is an incomplete list.
- "BIPM - measurement units". www.bipm.org. Retrieved 2018-04-26.
- "Criteria for membership of a Consultative Committee". Bureau International des Poids et Mesures. Archived from the original on 17 April 2012. Retrieved 25 September 2012.
- "BIPM - CIPM Outcomes". www.bipm.org. Retrieved 2018-12-11.
- "BIPM - official reports". www.bipm.org. Retrieved 2018-04-26.
- "CIPM: International Committee for Weights and Measures". Bureau International des Poids et Mesures. Retrieved 14 March 2013.
- Kovalevsky, J; Blevin, WR (March 1998). National and international needs relating to metrology : International collaborations and the role of the BIPM. Sèvres, France: Intergovernmental Organization of the Convention of the Metre. ISBN 92-822-2152-0. Retrieved 14 March 2013.
- Kovalevsky, J; Kaarls, R (April 2003). Evolving Needs for Metrology in Trade, Industry and Society and the Role of the BIPM (PDF). Sèvres, France: Intergovernmental Organization of the Convention of the Metre. ISBN 92-822-2212-8. Retrieved 14 March 2013.
- Taylor, Barry N., ed. (February 1991). "The International System of Units (SI): Approved translation of the sixth edition (1991) of the International Bureau of Weights and Measures publication Le Système International d'Unités (SI)" (PDF). NIST.
- International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), p. 102, ISBN 92-822-2213-6, archived (PDF) from the original on 2017-08-14