Piet Meijer is member of several national and international societies in the field of thrombosis and haemostasis [International Society for Thrombosis and Haemostasis (ISTH), Dutch Society for Thrombosis and Haemostasis (NVTH), Australian Society for Thrombosis and Haemostasis (ASTH), German Society for Thrombosis and Haemostasis (GTH), International Society for Laboratory Haematology (ISLH)] and External Quality Assessment [European Association for Quality Assessment Organizations in Medical Laboratories (EQALM), International Association for External Quality Assessment in Thrombosis and Haemostasis (EQATH)]. He is vice-chair of the steering committee of EQATH.

 He is expert member of the EQALM/EFLM Post-Analytical Working Group. He is member of the ICSH (International Committee of Standardization in Haematology) steering group on haemostasis and member of several guideline groups. He is international advisor for the ProMeQuaLab project (quality improvement in medical laboratories in Portuguese-speaking developing countries). He is member of the IFCC/ISTH Working Group on PT/INR Standardization. Currently he chairs the EQALM Working Group on the EQALM Central Database and as such also be part of the HALMA initiative (HArmonization of measurands in Laboratory Medicine through data Aggregation). He also represents EQALM in JCTLM (Joint Committee on Traceability in Laboratory Medicine). .