This workshop service repair manual covers Volvo Penta MD21A, AQD21A, MD32A, and AQD32A marine diesel engines, designed for marine propulsion. These diesel engines are engineered for reliability and performance in demanding marine environments. This manual provides comprehensive information for maintaining and repairing these essential marine propulsion units, ensuring their optimal function. This English-language manual is intended for a wide audience, from first-time owners to professional technicians. It details routine maintenance procedures, including lubrication, cooling, and fuel systems, to prevent premature failure and save time and money. The manual also includes a fault-tracing system, special tools information, and detailed technical specifications, covering engine assembly, electrical systems, and more, to facilitate effective troubleshooting and repair.