We define productive biofilms as microbial communities utilised in biotechnological processes as biocatalysts for the production of value-added chemicals. For successful implementation, it is essential to merge engineering and natural sciences to equally address biological aspects like biofilm growth, structure and physiology, as well as technical challenges like reactor configuration, mass transfer issues and scale up. Productive biofilms growing on active substrate like membranes (delivering gaseous substrates) or electrodes (acting as electron donor or acceptor) are perfect model systems to study the benefits, challenges and limitations of continuous productive biofilm systems. Hence, we welcome contributions that present new processes and/or biocatalysts thriving on active substrata, describe new solutions for reactor design or highlight the impact of the biofilm matrix and heterogeneity on productivity.