ARIES is an EU-sponsored programme for accelerator research and innovation. An international workshop was held online as part of this programme in June 2021 on the topic of 'Materials and Engineering Technologies for Particle Accelerator Beam Diagnostic Instruments'. The aim of the workshop was to bring together instrument designers, experts and industry and research groups to review the state of the art in the field, present designs and discuss future challenges, whilst also developing and strengthening collaborations between groups. There were sessions covering 'Instrument design and operation', 'Novel materials and applications' and 'New technology and components' over the three half-days of the online meeting. This paper reviews the key topics presented at the workshop.