The present invention relates to substrates comprising a crosslinked network of covalently attached antimicrobial and/or antibiofouling polymers. The crosslinked network of antimicrobial and/or antibiofouling polymers acts highly efficiently against pathogens, e.g. bacteria and fungi. Both the antimicrobial and the antibiofouling cross-linked polymer networks are preferably better resistant to mechanical damage than simple surface-immobilized polymer monolayers. The antimicrobial and/or antibiofouling polymers of the crosslinked network are preferably obtained by ring opening metathesis polymerization (ROMP) and exhibit a molecular weight of preferably more than 30,000 or even 100,000 g mol-1. The crosslinked network of antimicrobial and/or antibiofouling polymers is preferably covalently attached to the surface of a substrate, e.g. an implant, a medical device, medical equipment or a (tissue-supporting) biomaterial, etc. The present invention is also directed to uses of crosslinked networks of antimicrobial and/or antibiofouling polymers as defined herein, e.g. for coating a surface of a substrate, and to methods therefore.