Book excerpt: This Special Issue Book, “Marine Bioactive Peptides: Structure, Function, and Therapeutic Potential" includes up-to-date information regarding bioactive peptides isolated from marine organisms. Marine peptides have been found in various phyla, and their numbers have grown in recent years. These peptides are diverse in structure and possess broad-spectrum activities that have great potential for medical applications. Various marine peptides are evolutionary ancient molecular factors of innate immunity that play a key role in host defense. A plethora of biological activities, including antibacterial, antifungal, antiviral, anticancer, anticoagulant, endotoxin-binding, immune-modulating, etc., make marine peptides an attractive molecular basis for drug design. This Special Issue Book presents new results in the isolation, structural elucidation, functional characterization, and therapeutic potential evaluation of peptides found in marine organisms. Chemical synthesis and biotechnological production of marine peptides and their mimetics is also a focus of this Special Issue Book.