Abstract: Resilience and sustainability are two primary objectives for future cities. The violent consequences of extreme natural events and the environmental, social and economic burden of contemporary cities make the concepts of resilience and sustainability extremely relevant. In this paper we analyze the different definitions of resilience and sustainability applied to urban systems and propose a synthesis, based on similarities between the two concepts. According to the proposed approach, catastrophic events and the following transformations occurring in urban systems represent a moment in city lifecycle to be read through the complex sustainability framework. Hence, resilience is seen as a requirement for urban system sustainability. In addition, resilience should be evaluated not only for single cities, with their physical and social systems, but also on a global scale, taking account of the complex and dynamic relationships, connecting each other contemporary cities.