Society for General Microbiology CC BY 4.0 International http://creativecommons.org/licenses/by/4.0/ Guidelines for interpreting the International Code of Nomenclature of Prokaryotes and for preparing a Request for an Opinion International Journal of Systematic and Evolutionary Microbiology 73(3) (2023) In this paper the Judicial Commission provides general guidance for interpreting the International Code of Nomenclature of Prokaryotes (ICNP) and specific assistance to authors, reviewers and editors of a Request for an Opinion, or of other suggestions related to the ICNP. The role of the Judicial Commission is recapitulated, particularly with respect to the processing of such Requests. Selected kinds of nomenclature-related proposals are discussed that are unsuitable as the basis for a Request. Particular emphasis is put on Requests for placing names or epithets on the list of nomina rejicienda, and a dichotomous identification key is provided to guide potential authors of a Request that targets the name of a species or subspecies because of issues with its type strain. To this end, the criteria for the valid publication of such names under the ICNP are revisited. Aspects of other kinds of Requests are also addressed. The study is based on a comprehensive review of all Judicial Opinions issued since the publication of the Approved Lists in 1980. One goal of this paper is to assist potential authors in deciding whether their concern should be the subject of a Request, and if so, in composing it with the greatest chance of success. It is also clarified how to obtain additional help regarding nomenclature-related issues. 2023 article Phylogeny; Sequence Analysis, DNA; RNA, Ribosomal, 16Sgenetics; DNA, Bacterial Genetics; Bacterial Typing Techniques; Base Composition; Fatty Acids Chemistry Arahal, David R. (Universitat de València) Göker, Markus (Leibniz Institute DSMZ – German Collection of Microorganisms and Cell Cultures) Bull, Carolee T. (Pennsylvania State University) Busse, Hans-Jürgen (University of Veterinary Medicine Vienna) Ventosa, Antonio (Universidad de Sevilla) Rossello-Mora, Ramon (Institut Mediterrani d'Estudis Avançats) Parker, Charles T. Konstantinidis, Konstantinos T. (Georgia Institute of Technology) Fournier, Pierre-Edouard (Méditerranée Infection Foundation) Dedysh, Svetlana N. (Research Center of Biotechnology RAS) Chuvochina, Maria (University of Queensland) Christensen, Henrik (University of Copenhagen) application/pdf eng doi:10.1099/ijsem.0.005782 https://phaidra.vetmeduni.ac.at/o:3376