Carbon monoxide (CO)-containing process gases, abundant in the BIG-Cluster region of Flanders, The Netherlands and North-Rhine Westphalia through numerous industrial sites, can be valuable feedstock streams for the biotechnical production of building blocks that are currently produced via petrochemical process routes. Mid-chain carbon compounds with multifunctional groups are of special industrial interest. Since they are conventionally generated from fossil resources, routes using renewable non-food feedstocks to provide such precursors would be a major step to establish a sustainable economy. Therefore, BioCOnversion aims at developing and implementing a sustainable process from CO to a defined polymer precursor by evaluating different technologies. An international consortium of industrial and academic partners join their high-level, multidisciplinary expertise to develop a process comprising the primary conversion of CO/syngas into an intermediate through gas fermentation and its enzymatic upgrading conversion to the defined plastic precursor. BioCOnversion supports the BIG-Cluster efforts to transform the trinational region of the German state of North Rhine-Westphalia, the Netherlands and the Belgian region of Flanders into a world-leader of circular economy.