The World Health Organization brings together international experts in specific fields through its biological standardization programme to develop and revise specific recommendations for the production and quality control of vaccines of major international public health importance. Authoritative, harmonized guidelines and recommendations, for use by manufacturers and regulatory authorities, are published in the reports of ECBS meetings in the WHO Technical Report Series. These include recommendations for individual vaccines, and also more general guidelines on technical or regulatory topics such as cell substrates, nonclinical evaluation, or clinical evaluation. This programme also establishes and distributes the WHO Biological Reference Materials required for the standardization of assays to laboratories around the world such as manufacturers and National Control Laboratories (NCLs) who are involved in the quality control of vaccines. This activity is critical to ensure the quality of essential vaccines in a global market.