The design of machining lines is a wide open area for development and application of decision making and optimization technologies. This domain is characterized by the necessity to combine the standard decision making methods, sophisticated operational research techniques and some specific rules based on expert knowledge to take into account principal technological constraints and criteria. A promising trend in this area deals with the development of integrated decision aid tools. Their main idea consists in integrating product and manufacturing data into a common database. This enables product designers to consider the manufacturing processes constraints at the early product design stage. At the same time, all data of product design should be used directly for optimizing the corresponding machining line. That’s why the core of these software tools is a powerful extendable database, supported by a user friendly software environment. This database normally contains digital models of product and processes. In order to find an optimal manufacturing system configuration, a set of advanced optimization techniques, decision making and decision support methods are used. We present the main principles and ideas of decision making by the example of decision and support soluton for machining lines used in the automotive industry. The suggested approach is based on several techniques: -powerful database of standard solutions and efficient mecanisms to search the existing elements; -expert system to choose better solutions from database; -line balancing model based on different optimisation approaches; -set of problem oriented rules; -user friendly software environment. These techniques are combined in the decision support software tool for optimal process planning, line balancing and equipement selection for optimal design of machining lines for the automotive industry.