Dr E. F. Arias is a member of the IAU, participating in three of its working groups: on nutation; on the international celestial reference system; and on the redefinition of UTC. She is an associate member of the IERS, a member of the ICRS Product Centre and of the Conventions Product Centre of the IERS. She is a member of the IVS, and of its Analysis Working Group on the International Celestial Reference Frame. She is the BIPM representative at the Governing Board of the IGS and the Action Team on GNSS of COPUOS. She is a member of the Argentine Council of Research (CONICET) and an associate astronomer at the SYRTE, Paris Observatory. She is a corresponding member of the Bureau des Longitudes. She is currently the BIPM representative on the governing board of the International GPS Service (IGS). She is the BIPM representative to Working Party 7A of Study Group 7 of the ITU-R, and a member of its Special Rapporteur Group on the future of UTC.

Dr W. Lewandowski is the BIPM representative to the Civil GPS Service Interface Committee (CGSIC), and chairman of its Timing Subcommittee. He is also a member of the Scientific Council of the Space Research Centre, Polish Academy of Sciences.

Dr G. Petit is co-director of the Conventions Product Centre of the IERS and representative to the Directing Board of the IERS. He is a member of the IAU Working Group on Relativity in Celestial Mechanics, Astrometry and Metrology (RCMAM), the IGS Working Group on Clock Products, the Comité National Français de Géodésie et Géophysique (CNFGG), and the Fundamental Physics Group of the CNES.

Dr P. Wolf is a member of the IAU Working Group on Relativity in Celestial Mechanics, Astrometry and Metrology (RCMAM), the GREX (Gravitation and Experiment Research Group of the CNRS), and the Fundamental Physics Group of the CNES.

E.F. Arias is Executive Secretary of the CCTF. She is a member of the CCTF Working Group on Two-Way Satellite Time and Frequency Transfer (TWSTFT).

W. Lewandowski is secretary of the CCTF Working Group on TWSTFT and secretary of the CCTF Working Group on Global Navigation Satellite Systems Time-Transfer Standards (CGGTTS).

G. Petit is a member of the CCTF Working Group on TAI and its Sub-Group on Algorithms, and of the CGGTTS.