Heterogeneity is the most reliable companion of biofilm development in all types of environments. Structural heterogeneity can be described by parameters like texture, roughness, and porosity among others. Variations in these parameters are often indicative of the performance of biofilm systems in terms of turnover, substrate consumption, and mass transfer at the biofilm-water interface. Hence, structural heterogeneity will often correlate with heterogeneity on a molecular level. Challenges appear if we want to predict the amount of substrate, which can be converted or the amount of product, which can be generated by a biofilm of a certain surface area over time. We would like to approach the term heterogeneity in biofilm systems with advanced imaging techniques both on the micrometre scale but also on the mesoscale with molecular techniques like single cell sequencing. Moreover, we would like to have contributions which can show that heterogeneity can be quantified and linked to biofilm performance measures.