Agarase plays a key role in the high-value utilization of marine red algae polysaccharide resources, and it has attracted wide attention in recent years. This chapter reviews the research progress of agarase in detail, including the sources and classification, enzyme activity assay, biochemical properties, degradation patterns, structure and action mechanism, preparation and modification strategies, and applications of agarases. This part aims to help researchers fully grasp the research trends of agarose and expand the application scope of this enzyme.