Existing methods of joining automotive aluminium alloys are either expensive (Self Pierce Rivets) or di cult to implement (Resistance Spot Welding). Ultrasonic spot welding (USW) is a new alternative method using ~2% of the energy of resistance spot welding. USW is a solid state welding process that combines vibration and pressure at the interface of a joint to produce a weld. Much of the existing research focuses testing under laboratory conditions, using simple coupon sample geometry, and has proven to be an extremely robust process. This thesis shows a detailed investigation into the implementation of USW on automotive body panels, in collaboration with Jaguar Land Rover. Weld performance, bonding mechanisms and temperature gradients found in AA5754 align well with other research conducted using 6XXX series aluminium alloys. A laboratory trial was completed to verify all joints could be achieved on a Jaguar XJ dash panel, followed by installation of a USW machine in a production cell. A detailed statistical analysis was performed on strength and sticking data gathered from 60 Jaguar XJ dash panels that were welded in the trial. Results showed difficulty to apply USW in certain areas of the panel, although previous trials had suggested it was possible. A collaboration with Ford Motor Company allowed research to be conducted at the Ford Research and Innovation Center. Experiments were designed to discover which elements of the USW equipment had the most profound effect on weld strength, and a full factorial Design of Experiments was produced to and the most effective method of reducing variation in weld strength. Results showed that the vibrational response of complex geometry parts makes USW very difficult to predict, making it difficult to successfully implement in the automotive industry.