The need to develop software at Internet speed and accommodate changes during the entire software development life cycle has made lightweight or agile development methodologies like Extreme Programming popular. However, such methodologies have been considered to be beneficial for small and medium sized projects, with small teams. In this research, based on a case study in an organization that develops large-scale, complex software using a modified form of extreme programming, we highlight the key differences between agile principles proposed in prior literature and the agile practices that are suitable for large-scale, complex software development. Based on these differences, we propose general guidelines on tailoring agile development methodologies to make them suitable for the development of large, complex software systems .