FDA 21 CFR Part 820 is a set of regulations by the US FDA that ensures medical devices are designed, manufactured, and distributed safely and effectively. It requires manufacturers to establish and maintain a Quality Management System (QMS) covering design, production, labeling, and more. Compliance helps prevent defects, improves product quality, and is mandatory for selling medical devices in the US. Manufacturers must follow specific steps like understanding the rules, implementing the QMS, training staff, conducting audits, and correcting issues to meet these requirements.