The capability to dynamically adapt in-progress workflows (WF) is an essential requirement for any workflow management system (WfMS). This fact has been recognized by the WF community for a long time and different approaches in the area of adaptive workflows have been developed so far. This survey systematically classifies these approaches and discusses their strengths and limitations along typical problems related to dynamic WF change. Along this classification we present important criteria for the correct adaptation of running workflows and analyze how actual approaches satisfy them. Furthermore, we provide a detailed comparison of these approaches and sketch important further issues related to dynamic change.