This research develops, tests and refines an implementation model with the supporting toolkit to implement business process and IT systems within an existing manufacturing environment. The implementation model is based on the vehicle development process and the IT systems development process. A supporting toolkit has been developed by reviewing multiple areas of research and practice such as project management, quality management, systems engineering, behavioural studies, business process reengineering, people and cultural studies, as well as best practices within industry. This model and its corresponding toolkit has then been thoroughly tested and refined based on empirical research and experiences gained within 3 business cases, which took place within the BMW Group between 1996 and 2001. Due to the growth of joint ventures, mergers and acquisitions within the automotive sector the introduction on new business processes and IT systems represents a common problem within the automotive and other industries. Common business processes and IT systems within one automotive group enable the flexible use of manufacturing capacity and skilled workforce. Thus they represent the way to realise the synergy potential that often drives mergers and acquisitions. Within the business cases which are focused in this research, the introduction of new business processes and IT systems in the areas of engineering, sales and marketing, production, finance and process planning was carried out in parallel with the introduction of a new product. The challenges of such programmes are multiplied and the price of failure is tremendous. At the BMW Group the knowledge or model and toolkit of how to manage such a wide-ranging business change was not available when the first business case was initiated. Thus it had to be developed and documented on the run based on the lessons learnt. This research helped to enable and structure this process. Key recommendations for successful implementation are proposed. Critical people and cultural issues when implementing new business processes and IT systems are analysed and strategies for their resolution are proposed. With this research an overarching, holistic model on business process and IT systems implementation and the required toolkit is provided. Both theoretical research and practical experiences within an industrial context are linked due to the unique set-up of this research. This research set-up and the fact that the results were generated within the BMW Group facilitated the acceptance and the diffusion of the recommendations within the BMW Group. Principal parts of this model and its toolkit are now being used at the BMW Group on current business cases. The pre-study duration (Time-to-decision) and the duration of the implementation were halved. Future programmes will benefit from the results of this research.