The CONUL Research Group sponsored a workshop on the certification of digital repositories, focusing on the CoreTrustSeal framework. The workshop was presented by Dr John B Howard of University College Dublin, a founding member of the CoreTrustSeal Board of Directors. The workshop reviewed the concept of "trust" in the context of data management and Open Science, identifying stakeholders and the issues that identify trustworthiness as a significant issue for managers of digital repository services. An overview of initiatives and services that provide a basis for the certification of digital repositories will be provided, including the European Framework for Audit & Certification of Digital Repositories. Focus was made on the CoreTrustSeal, a framework that represents a merger of the previously separate Data Seal of Approval and ICSU/World Data Systems assessment and certification approaches. Attendees were introduced to the assessment process and requirements, including a walk through the 17 assessment categories in the CTS questionnaire.