The EOSC-ENTRUST project aims to create a European Network of Trusted Research Environments (TREs). One task in this 3-year project is to establish a machine-readable TRE Provider catalogue, listing available TREs and their respective capabilities. Towards the end of the project, this EOSC-ENTRUST TRE Provider Catalogue (short: catalogue) shall be made accessible as part of the EOSC federation offering. The catalogue will depend on service providers to populate it with detailed descriptions of their service capabilities to allow a comparative analysis of technical capabilities and identification of gaps between environments. The public version of the catalogue will give potential users of these services a tool to map their secure processing environment requirements to the available solutions. In this report, we describe the steps taken to create the first edition of the catalogue (D13.3). This deliverable takes input from the first edition of the EOSC-ENTRUST TRE Inventory provided by the EOSC-ENTRUST TRE Provider Forum work package (WP10). The chosen format for this initial version of the catalogue is a spreadsheet. In the future, it will be developed for more detailed and technically advanced versions that will serve multiple use cases. The second catalogue edition is scheduled to be delivered in autumn 2025 and the final one in autumn 2026.