Mussels of the genus Mytilus are ecologically and commercially important worldwide, and they form hybrid complexes where their distributions overlap. Allozyme and nuclear markers have bee It Used to investigate their genetics over many years, but successful development of reliable highly valuable microsatellite markers has lagged be hind other shellfish species. We have developed and characterized tell novel microsatellite loci that amplify reliably for the blue mussel Mytilus edulis. The number of alleles among 30 individuals from a wild population (Menai Strait, North Wales UK) ranged between 9 and 29 and the observed heterozygosity between 0.300 and 0.954. Significant heterozygote deficiencies against the Hardy-Weinberg model were observed at 6 out of 10 loci. Analyses using MICRO-CHECKER suggested the presence of null alleles at 8 out of 10 microsatellites with estimated null allele frequencies ranging front 0.105-0.305. The 10 newly developed microsatellites will have value to discriminate between Mytilus species, to support studies of introgression and hybridization and to strengthen and improve the available genetic linkage map.