In parallel with the observed greater frequency of natural disasters worldwide, there has been an ever-increasing interest in urban resilience and its assessment. Experience obtained in recent extreme events (in particular, earthquakes and floods) has revealed that both the level of preparedness and the response of affected cities were insufficiently high, whereas the recovery process was long and expensive. For this reason improved pre-disaster mitigation actions, as well as smart and strategic urban planning in threatened areas (e.g. in earthquake-prone regions), is essential. For this purpose, a comprehensive review of the existing literature has been performed in relation to the holistic assessment of urban system resilience to natural disasters, with an emphasis on the effect of earthquakes. The main goal of the review was to try to determine how to best assess the resilience of urban systems as a whole, taking into account all of their components, i.e. both the physical components (i.e. of buildings, infrastructure, and open spaces) and the social components (i.e. of the community), as well as the dynamic interactions between them. Besides considering the commonly measured indicators (e.g. determination of the scope of actual structural damage caused by an earthquake), the paper tries to extend the discussion to some indicators which are not so commonly taken into account, by applying a quantitative resilience assessment approach. Based on the results of the described new literature review, a preliminary concept which could be used to assess the seismic resilience of complex urban systems, taking into account all urban components which have been identified as having an important impact on the latter, is presented. This concept consists of three different parts: (i) a probabilistic fragility analysis for each individual physical element (i.e. a building or an infrastructure element), (ii) a composite index methodology for the measurement of community disaster resilience, and (iii) a complex network approach (graph theory) for the assessment of the resilience of urban systems as a whole. Since, in the existing literature, there is a lack of consideration of urban open space, which can have a significant role in the recovery process, it is suggested that, in future research of seismic resilience assessment, such open space should be taken into account, and that an in-depth study of possible recovery strategies be performed.