Context From June 2020 to February 2021, a consortium of 10 organisations undertook a large-scale study on open access journals across the world that are free for readers and authors, usually referred to as “OA diamond journals”. This study was commissioned by cOAlition S in order to gain a better understanding of the OA diamond landscape. Presentation The study undertook a statistical analysis of several bibliographic databases, surveyed 1,619 journals, collected 7,019 free text submissions and other data from 94 questions, and organised three focus groups with 11 journals and 10 interviews with hosting platforms. It collected 163 references in the academic literature, and inventoried 1048 journals not listed in DOAJ. The results of the study are available in the following outputs: Findings Report - DOI: 10.5281/zenodo.4558704 Recommendations Report- DOI:10.5281/zenodo.4562790 References Library - DOI: 10.5281/zenodo.4562816 Journals Inventory - DOI: 10.5281/zenodo.4562828 Dataset - DOI: 10.5281/zenodo.4553103 This dataset contains data used by and partly generated by the OA Diamond Journals Study on open access journals that do not charge authors. It contains the data files themselves as well as some readme texts with variable lists. Available files: Survey questionnaire, English version (PDF) Survey data without identifying information and without free texts answers (as these might also include identifying information) (CSV). This includes, for some questions, data from DOAJ for journals present in that database. Readme text with the variable list for the survey data file (TXT) Stratified sample of 500 records from the ROAD database of open access journals downloaded 20201102 (CSV) Readme text with the variable list for the ROAD database sample (TXT) Directory of Open Access Journals (DOAJ) metadata downloaded 20200602 (CSV) Directory of Open Access Journals (DOAJ) metadata downloaded 20200918 (CSV) Added and Removed change log DOAJ, downloaded 20210121 (CSV) Readme text with variable list for the Added and Removed change log DOAJ (TXT) All data are available for reuse under a CC0 license. Additionally, an online version of the survey results (excluding DOAJ data and excluding free text answers) is available from SurveyMonkey