The validation of built-up areas derived from different sensors is crucial for gaining a deeper understanding of the consistency and interoperability between them. This article presents the methodology and results of an inter-sensor comparison of built-up area data derived from Landsat, Sentinel-1, Sentinel-2, and SPOT5/SPOT6. The assessment was performed for 13 cities across the world for which cartographic reference building footprints were available. Several validation approaches were used: cumulative built-up curve analysis, pixel-by-pixel performance metrics, and regression analysis. The results indicate that Sentinel-1 and Sentinel-2 contribute greatly to improved built-up area detection compared to Landsat, within the global human settlement framework. However, Sentinel-2 tends to show high omission errors while Landsat tends to have the lowest omission error. The built-up area obtained from SPOT5/SPOT6 shows high consistency with the reference data for all European cities, and hence can potentially be considered as a reference dataset for wall-to-wall validation in Europe.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.Knowledge of the spatial distribution of human settlements and monitoring of urban expansion are crucial for a large number of applications, such as exposure mapping and risk assessment, infrastructure planning, biodiversity conservation, climate change, and urban development (Chrysoulakis et al., 2014;Triantakonstantis et al., 2015;Florczyk et al., 2016). One key for understanding worldwide urbanization processes and developing actions toward sustainable urban and rural development is the availability of detailed, up-to-date, accurate, and consistent-in time and space-information on human settlements. Human settlements are closely related to population distribution, as well as to social and economic development which, from the spatial perspective, is not directly measurable. Built-up areas, which refer to the physical space used for human habitation, represent the physical dimension of human settlements and the most appropriate surrogate for urbanization processes. The spatial aspect involved in the definition of built-up areas is what makes remote sensing appealing for extracting global and up-to-date information on the extent of the built-up environment that can be related directly to human settlements.