Background: As of September 2022, there was no globally recommended set of core data elements for use in multiple sclerosis (MS) healthcare and research. As a result, data harmonisation across observational data sources and scientific collaboration is limited., Objectives: To define and agree upon a core dataset for real-world data (RWD) in MS from observational registries and cohorts., Methods: A three-phase process approach was conducted combining a landscaping exercise with dedicated discussions within a global multi-stakeholder task force consisting of 20 experts in the field of MS and its RWD to define the Core Dataset., Results: A core dataset for MS consisting of 44 variables in eight categories was translated into a data dictionary that has been published and disseminated for emerging and existing registries and cohorts to use. Categories include variables on demographics and comorbidities (patient-specific data), disease history, disease status, relapses, magnetic resonance imaging (MRI) and treatment data (disease-specific data)., Conclusion: The MS Data Alliance Core Dataset guides emerging registries in their dataset definitions and speeds up and supports harmonisation across registries and initiatives. The straight-forward, time-efficient process using a dedicated global multi-stakeholder task force has proven to be effective to define a concise core dataset., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: T.P. has no other conflicts of interests to disclose than that she is funded by the Flemish Government under the ‘Special Research Fund (Bijzonder Onderzoeksfonds, BOF)’: BOF22OWB01. L.G. has no other conflicts of interests to disclose than that she is funded by the Flemish Government under the ‘Onderzoeksprogramma Artificiële Intelligentie Vlaanderen’. A.H. has no personal pecuniary interests to disclose, other than being an employee of the MS International Federation, which receives income from a range of corporate sponsors, recently including: Biogen, BristolMyersSquibb, Coloplast, Janssen, Merck, Viatris (formerly Mylan), Novartis, Roche and Sanofi – all of which is publicly disclosed. J.H. has received honoraria for serving on advisory boards for Biogen, Bristol-Myers-Squibb, Sanofi-Genzyme, Merck KGaA, Novartis, and Sandoz and speaker’s fees from Biogen, Novartis, Merck KGaA, Teva and Sanofi-Genzyme. He has served as P.I. for projects, or received unrestricted research support from, Biogen, Bristol-Myers-Squibb, Merck KGaA, Novartis, Roche and Sanofi-Genzyme. His MS research was funded by the Swedish Research Council and the Swedish Brain foundation. H.S. works for the Accelerated Cure Project for MS (ACP), which has received grants, collaboration funding, payments for use of assets, or in-kind contributions from the following companies: EMD Serono, Sanofi/Genzyme, Biogen, Genentech, AbbVie, Octave, GlycoMinds, Pfizer, MedDay, AstraZeneca, Teva, Mallinckrodt, MSDx, Regeneron Genetics Centre, BC Platforms, and Celgene. A.C.P. has also received funding from the Patient-Centred Outcomes Research Institute (PCORI) and the National MS Society (NMSS). A.S. is on the editorial board for Neurology and serves as a consultant for Gryphon Bio, LLC. She has received research funding from the Department of Defence, MS Society of Canada, National MS Society and the Consortium of MS Centres. A.S. works for the NARCOMS Registry which is supported by the Consortium of MS Centres (CMSC) and the Foundation of the CMSC. R.M. has received no personal funding from any sources, the UK MS Register is funded by the MS Society, and has received funding for specific projects from Novartis, Sanofi-Genzyme, and Merck KGaA. A.S. has no personal pecuniary interests to disclose, other than being the lead of the German MS-Registry, which receives funding from a range of public and corporate sponsors, recently including: The German Innovation Fund (G-BA), The German MS Trust, The German Retirement Insurance, German MS Society, Biogen, Celgene (BMS), Merck, Novartis, Roche and Sanofi. P.D. is a full-time employee and a shareholder of Biogen. E.H.M.-L. and K.P. have no conflicts of interest to disclose. The views expressed in this article are the personal views of the author(s) and may not be understood or quoted as being made on behalf of or reflecting the position of the EMA or one of its committees or working parties. P.I. has served on scientific advisory boards for Biogen Idec, Bayer, Teva, Roche, Merck Serono, Novartis and Genzyme and has received funding for travel and/or Speaker honoraria from Sanofi Aventis, Genzyme, Biogen Idec, Teva, Merck Serono, Alexion and Novartis. J.I.R. has received honoraria from Novartis as a scientific advisor. He has received travel grants and attended courses and conferences on behalf of Merck-Serono Argentina, Novartis, Roche, Sanofi-Genzyme, Biogen, Bayer and Teva. He receives unrestricted research funding from Novartis, Biogen, Roche, Merck and Sanofi. M.M. has served in scientific advisory board for Sanofi, Novartis, Merck, and has received honoraria for lecturing from Biogen, Merck, Novartis, Roche, Genzyme, Bristol-Myers Squibb. She received research support and support for congress participation from Biogen, Genzyme, Roche, Merck, Novartis. A.v.d.W. has received honoraria and unrestricted research funding from Novartis, Biogen, Roche, Merck and Sanofi. G.C. reports that he has received consulting and speaking fees from Novartis, Teva Pharmaceutical Industries Ltd, Teva Italia Srl, Sanofi-Genzyme Corporation, Genzyme Europe, Merck KGgA, Merck Serono SpA, Celgene Group, Biogen Idec, Biogen Italia Srl, F. Hoffman-La Roche, Roche SpA, Almirall SpA, Forward Pharma, Medday, and Excemed. L.M.P. has no conflict to report related to this work other than being the chair and the coordinator of the MSDA initiative, receiving funding from a range of corporate sponsors, including Biogen, Bristol-Myers Squibb, Janssen Pharmaceuticals, Merck, Novartis, and Roche. All other co-authors have no relevant competing interests to report. The authors declare that the funding sources did not influence the content of this work.