Cross-national Social Sciences survey FAIR implementation case studies report. Project Deliverable D6.1 for EC WIDERA-funded project "WorldFAIR: Global cooperation on FAIR data policy and practice". This report provides an overview of the data harmonisation practices of comparative (cross-national) social surveys, through case studies of: (1) the European Social Survey (ESS) and (2) a satellite study, the Australian Social Survey International – European Social Survey (AUSSI-ESS). To do this, we compare and contrast the practices between the Australian Data Archive and Sikt.no, the organisations responsible for the data management of ESS and AUSSI-ESS. The case studies consider the current data management and harmonisation practices of study partners in the ESS, including an analysis of the current practices with FAIR data standards, particularly leveraging FAIR Implementation Profiles (FIPs) and FAIR Enabling Resources (FERs). The comparative analysis of the two case studies considers key similarities and differences in the management of the two data collections. Core differences in the use of standards and accessible, persistent registry services are highlighted, as these impact on the potential for shared, integrated reuse of services and content between the two partner organisations. The report concludes with a set of recommended practices for improved management and automation of ESS data going forward—setting the stage for Phase 2 of WorldFAIR Work Package 6—and outlines the proposed means for implementing this management in the two partner organisations. These recommendations focus on three areas of shared interest: Aligning standards Establishing common tools Establishing and using registries in order to advance implementation of the FAIR principles, and to improve interoperability and reusability of digital data in social sciences research. Visit WorldFAIR online at http://worldfair-project.eu. WorldFAIR is funded by the EC HORIZON-WIDERA-2021-ERA-01-41 Coordination and Support Action under Grant Agreement No. 101058393.