This report defines the audiences, expected changes, principles, and actions of DiSSCo advocacy strategy for country engagement. The strategy's main objective is to obtain national commitment to DiSSCo's construction and operation phases. This should be a long-term financial and political commitment based on DiSSCo's position as a large-scale pan-European research infrastructure of national interest. For that, the advocacy strategy establishes cooperation between the DiSSCo CSO and the WP8 leader CETAF to foster the involvement of DiSSCo NNs, and Funders Forum representatives with a twofold objective: (1) to build tailored advocacy strategies at the national level that ensures national commitments for the operation of DiSSCo, and (2) to help shape the strategic and organisational developments of the research infrastructure during its preparatory phase, based on the partnership involved.