Contemporary Information Systems Development (ISD) takes place in a dynamic environment and is generally acknowledged as a complex activity. We investigate whether complex adaptive systems (CAS) theory is relevant as a theoretical foundation for understanding ISD, and if so, what kind of conception can be achieved by utilizing the theory? We introduce key CAS concepts and describe an emergent method framework for understanding ISD. Extending existing research, our main contribution is twofold: We first show how CAS and CAS principles are advantageous for comprehending and organizing ISD in general, beyond any particular development approach chosen for the execution of a project such as agile development. Thereby, we contribute to a complexity theory of ISD. Second, we back up our argument with a coherent empirical account of contemporary ISD, and thus contribute with practical advice for ISD derived from this perspective to successfully cope with complexity in ISD in an adaptive manner.