Herbicide resistant weeds are becoming increasingly common, threatening global food security. Here,we present BrIFAR: a new model system for the functional study of mechanisms of herbicide resistancein grass weeds. We have developed a large collection of Brachypodium accessions, the BrI collection, rep-resenting a wide range of habitats. Wide screening of the responses of the accessions to four majorherbicide groups (PSII, ACCase, ALS/AHAS and EPSPS inhibitors) identified 28 herbicide-resistance candi-date accessions. Target-site resistance to PSII inhibitors was found in accessions collected from habitatswith a known history of herbicide applications. An amino acid substitution in the psbA gene (serine264to glycine) conferred resistance and also significantly affected the flowering and shoot dry weight ofthe resistant accession, as compared to the sensitive accession. Non-target site resistance to ACCaseinhibitors was found in accessions collected from habitats with a history of herbicide application and froma nature reserve. In-vitro enzyme activity tests and responses following pre-treatment with malathion (acytochrome-P450 inhibitor) indicated sensitivity at the enzyme level, and give strong support to diclofop-methyl and pinoxaden enhanced detoxification as NTS resistance mechanism. BrIFAR can promote betterunderstanding of the evolution of mechanisms of herbicide resistance and aid the implementation ofintegrative management approaches for sustainable agriculture.