One objective of EUnetHTA’s (European Network for Health Technology Assessment) Joint Action 3 (JA3) is to set up a quality management system (QMS) for the joint work that serves as a standalone infrastructure for a sustainable European HTA (Health Technology Assessment) collaboration. The EU commission’s proposal, published in January 2018, on strengthening and defining the HTA collaboration after 2020 (the end of JA3) underlines the importance of a robust quality management (QM) in order to ensure the production of high-quality HTA-reports in Europe. High-quality HTA processes are characterized by being independent, transparent, complete and objective. Structures of the QMS (quality policy, processes and procedures and organizational structures) combined with the measures of QM (quality planning, assurance, control and improvement) both ensure achieving the quality objective. Processes, templates, methods and tools were already elaborated within previous Joint Actions. Based on re-evaluation, internal workshops and national expertise, the existing inventory is refined, complemented and revised within JA3. Procedures are gradually transferred into Standard Operating Procedures (SOPs), seamlessly and chronologically covering all phases of the assessment. These SOPs are supplemented by quality-control-checklists and helpful templates and are linked to relevant methodological guidelines and EUnetHTA-tools. To provide ultimate support and easy-to-access guidance to the assessment teams this knowledge conflates into the web-based “EUnetHTA Companion Guide”, which is accessible to the assessment teams since May 2018. The so-established QMS is subject to continuous improvement by recurrently applying the Deming-cycle. In order to identify the required adaptations, all assessment team members are systematically surveyed after the publication of each EUnetHTA-report. Process flows, SOPs, templates, guidelines and tools are further subject to modification, maintenance and improvement where deemed necessary.