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Purpose: Chronotyping is a key methodology for assessing individual differences in human adaptation to 24-h periodicity of geophysical and social environments. Throughout the 50-yr period of publications on chronotype questionnaires, there has been steady growth in number and diversity. Therefore, it is becoming increasingly difficult to determine which questionnaires can be optimally applied to address a given question in sleep and biological rhythm research. Consequently, this study aimed to develop a structured system for classifying and comparing chronotype questionnaires.Methods: The PubMed bibliographic database and 9 previously published reviews were searched for publications on chronotype questionnaires and/or their implementation in chronobiological and sleep studies.Results: A total of 75 questionnaires were identified, of which 60 and 15 were designed for only chronotype and chronotype and something else assessment, respectively. The proposed set of 20 questionnaire and questionnaire scale properties allows the distinction of any of the 60 questionnaires from the 59 other questionnaires.Conclusion: The structured system of questionnaire classification (“questionnaire identifier”) was proposed to help in navigating between numerous published questionnaires for choosing an optimal instrument for self-assessment of individual differences in a study of sleep and biological rhythms and for predicting properties of yet-unconstructed questionnaires.