Editorial European and International validation of 15 main reference methods in the microbiology of the food chain A large amount of qualitative and quantitative analytical results are produced internationally on a daily basis by laboratories involved in the microbiological testing of the food chain. These results are used by food business operators and risk managers to ensure food safety for consumers and fair trade of goods. To avoid the use of multiple methods for the same target, standardization bodies are developing and validating harmonised reference methods. Moreover, with quality management and accreditation of testing laboratories, it is widely accepted that only validated methods should be used to meet the customers' need of reliable results. At international level, it is the task of the SubCommittee 9 Microbiology of Technical Committee 34 Food products of ISO, the International Organization for Standardization (ISO/TC 34/SC 9). At regional level in Europe, Working Group 6 Microbiology of the food chain of the Technical Committee 275 Food analysis-Horizontal methods of CEN, the European Committee for Standardisation (CEN/TC 275/WG 6) is entrusted to this task (Leclercq et al., 2015). These two structures develop, validate and standardize common reference methods under the CEN/ISO Vienna agreement on technical cooperation. Until 1996, standardized reference methods were mainly based on recognized ex-perts' opinion or "historically proven" methodologies without performance characteristics derived from proper interlaboratory studies. The current policy of ISO/TC 34/SC 9 and CEN/TC 275/WG 6 requires a full validation of reference methods based on collaborative studies for inclusion of resulting performance characteristics in CEN/ISO standards (Anonymous, 2016c). In order to include performance characteristics in CEN/ISO standardized reference methods, a first European project, Project SMT4-CT96-2098 financed by European Commission under the fourth Framework Standards, Measurements and Testing Program (SMT4) was conducted between 1997 and 2000 to determine the performance characteristics (repeatability and reproducibility of quantitative methods or sensitivity, specificity, accordance and concordance of qualitative methods) of six CEN/ISO reference methods (De Buyser et al.). The determined performance characteristics have been included in the respective CEN/ISO Standards. They have allowed (i) risk managers to know the performance of the methods that are used in official controls to verify conformity of foodstuffs to legal micro-biological criteria, (ii) food operators to rely on methods used by food testing laboratories and fit for their purpose, (iii) food testing laboratories to verify their compliance to the method's performance characteristics in the frame of their EN ISO 17025 accreditation (Anonymous, 2005b), and (iv) validation/certification bodies to validate alternative proprietary methods against these reference methods, according to EN ISO 16140 and since 2016, EN ISO 16140-2 (Anonymous, 2003, 2016b). Further to the validation of these first 6 standardized reference methods and for similar purposes, European Commission signed a specific grant agreement in December 2010 with CEN (SA/CEN/ENTR/381/2010-06 in support of the CEN Mandate M/381) to finance the validation and standardization (or revision) of 15 methods for the main microorganisms (Bacteria: Campylobacter spp., Cronobacter spp., Enterobacteriaceae, Escherichia coli O157, Listeria monocytogenes, Salmonella spp., Vibrio cholerae, Vibrio parahaemolyticus, Vibrio vulnificus, pathogenic Yersinia enterocolitica, and Virus: norovirus, hepatitis A virus) or their toxins and metabolites in the field of food chain microbiology. These validations were in particular necessary to correctly set and implement microbiological criteria at European level, either already included in Commission Regulation (EC) No 2073/ 2005 (Anonymous, 2005a), or to be possibly included at a later stage in future amendments to this regulation (i.e. Norovirus, Hepatitis A, Bacillus cereus toxins). The 15 validation trials were carried out between 2012 and 2017 by a total of 150 laboratories in 35 countries with a budget of 3120000 euros, representing the largest worldwide validation effort of standardized methods in microbiology of the food chain. In this special issue, the detailed validation studies of each reference method are described in separate articles, except for the reference method for detection of staphylococcal enterotoxins. An harmonized experimental design for the organization of collaborative studies has been followed (Anonymous, 2010, 2014). The 15 reference methods which were validated are mostly microbiological methods, except two chemical methods, for quantification of histamine and Bacillus cereus toxins (cereulide) and one biochemical method, for detection of sta-phylococcal enterotoxins. Thus, two statistical approaches were used for the determination of performance characteristics: an approach designed for microbiological analysis and derived from EN ISO 16140-2 (Anonymous, 2016a, 2016b) and an approach more suited for chemical methods, derived from ISO 5725-2 (Anonymous, 1994).