Reducing structural weight in commercial aircraft is critical because it improves fuel efficiency, payload capacity, environmental performance, operating load, and maintenance cost. This study examines material selection criteria for lightweight aircraft design using the Boeing 777 family as a case study. Material selection depends on factors such as strength-to-weight ratio, stiffness-to-weight ratio, fatigue resistance, impact resistance, density, thermal stability, and manufacturability. The Boeing 777 demonstrates a balanced use of materials that meet functional requirements. Aluminum alloys are the primary structural material in the fuselage and framework due to low density, predictable fatigue behavior, and ease of maintenance.