The E/E (Electrical/Electronic) Architecture is the key enabler for new innovative user functions in the automotive domain. The E/E Architecture needs to manage the complexity of the E/E System in a cost-efficient manner. This is a fact for all domains developing mass-produced distributed systems containing embedded software. However, many companies in these domains are missing a clear description of the development process for E/E Architectures. In addition, the relation between development of E/E Architectures and the development of E/E Systems is not clear. This paper proposes a development process for E/E Architectures in the automotive domain. Furthermore, it shows the relation between development of E/E Architectures and development of E/E Systems. The development process is based on post mortem analysis of E/E System development projects conducted at an automotive company during the period 1998-2009, and it was validated in an E/E Architecture development project conducted during the period 2010-2011. The contribution of this paper is a detailed E/E System development process describing how to create and maintain an E/E Architecture and how to refine this into a Product-specific Architecture in Product development projects. Furthermore, the paper reports on experiences from working with RA development both as a small stand-alone company with few different products, and as part of a large global company with several different products.