This FDA final guidance (Version 2.0) establishes foundational principles for validating medical device software and software used in device design and manufacturing. The document systematically addresses software lifecycle methodologies, verification and validation (V&V) concepts, and documentation expectations. It defines key terminology including validation, verification, and testing, and describes the relationship between software development processes and regulatory submissions. Although IEC 62304 provides a more recent international standard framework, this guidance document remains a critical reference for FDA submissions and regulatory expectations. Manufacturers should apply the lifecycle principles outlined herein to demonstrate software safety and effectiveness. The guidance emphasizes that validation must be commensurate with device risk classification and intended use. It provides practical examples of validation approaches for various software categories and addresses both standalone software (SaMD) and software as a component of hardware devices. The document serves as essential foundational material for understanding FDA's expectations regarding software documentation in premarket applications.