: The design of engineering processes is dependent on the context they are designed for. This paper presents the results of an action research study that used design rationale to discover a number of contextual factors that provide criteria for designing a requirements engineering process in a given product line environment. The presented context dimensions and process design argumentation provide a starting point for understanding product line context and how supporting engineering processes are designed, communicated, and evaluated. Kewords: product lines, context, requirements engineering, process design, design rationale, action research