rsta.royalsocietypublishing.org Research Article submitted to journal Subject Areas: power system economics, power system security, power system planning & operation. Keywords: inter-TSO settlement, multi-area power systems, security management, grid flexibility. Author for correspondence: E. Karangelos e-mail: e.karangelos@uliege.be “Cooperative game” inspired approach for multi-area power system: day ahead – intraday markets & security management taking advantage of grid flexibilities Efthymios Karangelos 1 and Patrick Panciatici 2 1 Montefiore Institute - Department of EE & CS, Université de Liège, Liège, Belgium. 2 Reseau de Transport d’ Electricité (RTE), Paris La Défense, France. This paper advocates for a progressive rethinking of the day-ahead/intra-day power system security management practice in the low-carbon energy transition era. As a starting point, the need for multi-TSO coordination in order to efficiently exploit the value of grid flexibility towards operating the low-carbon, multi-area power system securely and economically is established. On this basis, the core proposal of this paper is the adoption of a new approach to day-ahead/intra-day multi-area power system security management, inspired from the principles of cooperative game theory. The proposed approach relies on counterfactual analysis to evaluate the (positive and/or negative) impact of each distinctive control-area to the common security of the multi-area system, thus providing clear economic incentives to achieve the required coordination. This proposal is not a marginal approach and notably facilitates the integration of more detailed physical modeling (including the non-convexities of the power system) in the inter-TSO settlement of the multi-area interconnected system security management cost. The proposed framework allows some level of subsidiarity and the definition of hedging products to cover ex- post costs. Further from the blueprint of the proposed approach, the paper discusses prominent research and development pathways in order to progressively put such vision into practice. c  The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/ by/4.0/, which permits unrestricted use, provided the original author and source are credited.