AUTOSAR introduces standardization of software development in three areas, namely Architecture, Application Interfaces and Methodology.The most frequently employed method for application SW migration is the Bottom-up approach, wherein the existing software architecture is reused with no or minimal change. This approach can introduce software performance and maintainability issues. Still, it is often preferred, as it is relatively easy to implement, because of experience with the architecture and the need for quick results.In the Top-down approach, on the other hand, the entire AUTOSAR architecture is created from a Vehicle System and Control System perspective. The Top-down method has potential for a superior result, although it is effort-intensive.A custom methodology for migration from a traditional SW architecture to AUTOSAR architecture is described in this paper. The approach seeks an optimum combination of the Top-down and the Bottom-up approaches to obtain a suitable compromise between the lower effort of the latter and the completeness of the former approach.The migration methodology is derived by unifying 1Standard architecture practices,2AUTOSAR architecture implementation methods, and3System Architecture KnowledgeThree levels of migration are defined in the proposed methodology: 1Level 0: Migration of traditional to AUTOSAR architecture with no implementation changes2Level 1: Migration by using re-factoring techniques for structural and implementation changes3Level 2: Migration by re-designing system, control architecture and Level 1 changesThe need for re-architecting the software to meet the architecture requirements is determined, both for the entire software and also for the individual software components. Following the up-front evaluation, the migration of the software is implemented at the required migration levels.