The contribution focuses on the current status of the ESA study entitled “INSARAP: Sentinel-1 InSAR Performance study with TOPS Data”. The study investigates the performance of the interferometric wide swath (IW) mode of Sentinel-1, which is implemented using the terrain observation by progressive scans (TOPS) mode. The key aspects of the TOPS mode that need to be considered for accurate interferometric processing will be presented, and first analyses with Sentinel-1 time series will be shown. The interferometric processing chain used to process the data will be expounded in detail. The interferometric results will focus on different pilot sites, namely, Campi Flegrei/Vesuvius area and Mount Etna, both located in Italy, Istanbul city in Turkey, and Mexico City. The evaluation of the results will be performed using in-situ geodetic measurements based on continuous GPS stations located on the different sites. For Mexico City and Istanbul a cross-check using TSX TOPS time series will be also used. Other relevant interferometric aspects will be also addressed, e.g., phase jumps due to azimuthal motion and ionospheric artefacts.