The Multi Material Lightweight Vehicle (MMLV) developed by Magna International and Ford Motor Company is a result of a US Department of Energy project DE-EE0005574. The project demonstrates the lightweighting potential of a five passenger sedan, while maintaining vehicle performance and occupant safety. Prototype vehicles were manufactured and limited full vehicle testing was conducted. The Mach-I vehicle design comprised of commercially available materials and production processes, achieved a 364kg (23.5%) full vehicle mass reduction, enabling the application of a 1.0-liter three-cylinder engine resulting in a significant environmental benefit and fuel reduction.This paper reviews the mass reduction and structural performance of aluminum, magnesium, and steel components for a lightweight multi material door design for a C/D segment passenger vehicle. Stiffness, durability, and crash requirements are assessed. The structure incorporated aluminum sheet, aluminum extrusion, magnesium high pressure vacuum die casting and steel sheet. The multi material components were assembled using structural adhesive bonding (hem and structure), self-pierce rivets (SPR's), single sided rivets, and bolts. The aluminum extrusion and the magnesium casting in the MMLV door were specifically designed to maximize stiffness, reduce part count and maximize mass reduction.To optimize the strength and weight of the MMLV door, a new aluminum intensive structure was developed. The new structure features a unique architecture that uses a multi-cavity aluminum extrusion joined to stamped sheet reinforcements to provide a direct load path between the hinges and the latch. The new structure also utilizes a high pressure vacuum die cast magnesium casting to create the structure at the base of the A-pillar on the front door to achieve the required structural stiffness while reducing components and maximizing the mass reduction. The “barn door” architecture of the inner structure of the door allowed for gauge optimization of the both the inner and outer stampings, the two largest and heaviest components of the assembly.Overall, the design architecture used in the MMLV doors allowed for a mass reduction of 33% through the use of multi material, gage optimization, and multiple forming technologies, while achieving all of the structural requirements.