Procedures set out in the standard operating procedures (SOPs) are followed by the IMD-PQS Secretariat, the IMD-PQS Working Group and by all technical specialists commissioned by the Secretariat. They are a useful source of information for manufacturers seeking prequalification of an immunization product since they describe and illustrate with examples the steps of a procedure, making it transparent for all stakeholders. They also indicate key responsibilities among those implementing the procedures.