XML data evolution has recently gained much interest in both research and practice. However, most of the existing works deal with separate aspects of the problem such as evolution of XML schemas or evolution of conceptual schemas and view the problem only from the perspective of a single application. In this paper we show that XML data evolution has several different levels at which it can be performed and that are highly related. Secondly, we show that evolution is not the problem of a single application, but multiple applications having the same problem domain can influence each other as well. We describe the particular levels, how they can be modified and the respective propagation of the modifications to other levels and applications.