R egulation (EU) 2019/1009 on Fertilising Products (FPR) allows the incorporation of industrial by-products in EU fertilising products if they meet the requirements of Component Material Category 11. The regulation also mandates the Commission to define safety and “agronomic efficiency” criteria for these by-products. This paper provides an indicative list of the primary industrial by-products that are used in the manufacture of plant biostimulants and highlights current difficulties for some of these by-products to be used under the future regulation as it is currently worded.  "