The Micro B3 checklist is a multi-disciplinary standard developed by the Micro B3 Consortium for description of marine microbial sampling. Content of the standard is grouped into six categories covering various aspects of marine microbial sampling. These categories are environment, measurement, sampling, event, sample and organism. Full adoption of the standard allows generation of data records, which are MIxS compliant but also compliant to minimal reporting requirements of the oceanographic and marine biodiversity community, i.e. respectively the Common Data Index (CDI) and the OBIS schema, advancing the metadata interoperability across research domains. Nucleotide sequences of marine microbial samples described according to the Micro B3 checklist can be placed into a very rich environmental context. This checklist had originally been called the M2B3 checklist