The Mediterranean mussel (Mytilus galloprovincialis) is a key species in European aquaculture, known for its economic and societal importance, particularly as a primary source of income for local fisheries in European coastal areas. While historically resilient to the mass mortality events that have affected other bivalve species, M. galloprovincialis may face increasing threats from emerging pathogens, including bacteria, viruses, and eukaryotic parasites. These microorganisms, often opportunistic, pose heightened risks in the current climate change scenario, where heatwaves are becoming increasingly frequent and the persistent presence of pollutants is suspected to impair the functional response of hemocytes. Over the past decade, significant advancements in immunological research have provided deeper insights into the cellular and molecular mechanisms underlying the robust defense system of M. galloprovincialis, which allows this species to efficiently cope with a broad range of infections. By analyzing the scientific literature published on mussel immunology over the past ten years, this review consolidates current knowledge on the immune system of the Mediterranean mussel. We place a particular focus on the cellular and molecular components involved in the recognition and elimination of microbial pathogens and discuss how the most recent discoveries may inform improved management and disease mitigation strategies for Mediterranean mussel farming in the in the years to come.