Biofilms develop in and on any wet substrate from mountainous rocks splashed by glacier-fed streams to deep-sea hydrothermal vents. Biofilms are not only hotspots of microbial diversity, but they also house astonishing abundances of meiofaunal organisms that find in a few-mm thick biofilm a proper shelter and a wealth of food items. This tiny ‘slimy universe’ represents a coherent and predictable framework to investigate responses of complex biological communities at convenient experimental scales. Therefore in this chapter, we proposed to explore three ques- tions to identify frontiers of meiofauna–biofilm research: (1) What are the Benefits of Living in the Slimy Universe? (2) How do Meiofauna Contribute to Biofilm Func- tions? (3) What are Applied Aspects of Research on Biofilm—Meiofauna? It appears that meiofauna is key players in biofilm food webs, obviously finding there a diver- sity of nutritive food items. However, studies should further investigate the feeding preferences of the meiofauna and their role in fluxes of energy to the upper-ends of those food webs (the macroscopic world). Biofilms offer shelter for meiofauna against flow erosion, desiccation, temperature fluctuation, UV-radiation and preda- tion. Whilst we have evidence of biofilm-compatible life-styles in some meiofaunal taxa like chromadorid nematodes, we lack knowledge on how the microbial world behaves when it is exposed to meiofaunal grazers. At small scales, meiofauna tends to stimulate biofilm functions both directly when grazing on some microbes and indi- rectly through poking holes in the cohesive matrix and through their excretion and secretions. However, to gain a comprehensive understanding of how benthos func- tions we urgently need to assess at a larger-scale, the consequences of meiofaunal control on microbially-mediated ecosystem processes. Finally, biofilm–meiofauna interactions show encouraging premices for a number of rewarding environmental applications like epuration of wastewater, remediation of xenobiotics, restoration of contaminated sites and consolidation of sediments.