The information generated in large organizations has been a great source of information for researchers, facilitating innovation and advances in various areas. Promoting an open and transparent approach has provided diverse benefits and competitive advantages for organizations. This dataset contains anonymized data from the CERN Mattermost service. The selected entities are Channel Information, Channel Member, Channel Member History, Teams, Team Members, and User. Document "CERN_Mattermost_OpenData_Tables.pdf" contains the data descriptions of data entities available from Mattermost before risk assessment and anonymization. Document "CERN_Mattermost_OpenData_Tables-Anonymus.pdf", contains data descriptions of data entities published within this dataset found in the "matermost.json" file. The dataset is released under the "CC BY-NC Creative Commons Attribution Non-Commercial Licence", to prevent the commercial application of the dataset, since the intent is to use the dataset for research purposes. The table below provides a brief overview of the data contained in the dataset: Description Value Number of Users 21231 Number of Teams 2367 Number of Buildings 151 Number of Organisational Units 163 Number of Channels 12773 A small framework to work with the CERN Anonymized Mattermost Data Set was created and can be reached via the following link: CERN Data Handling Framework (DOI: 10.5281/zenodo.6572538) Frequently Asked Questions What does it mean if a user does not have an Organisational Id and/or Building Id? This means that the User is an external user, for example a Guest Lecturer which has access to CERN Mattermost but is not part of an Organisational Unit or Building.