In this chapter, we give an overview of some of the most commonly used techniques for risk assessment of fault sealing and for induced seismicity. Fault sealing has long been a concern in reservoir/caprock engineering (Knipe in Structural and tectonic modelling and its application to petroleum geology. Elsevier, Stavanger, 1992; Ingram et al. in Hydrocarbon seals: Importance for exploration and production. Elsevier, Singapore, 1997). We first present two complementary methods used to estimate the across-fault and along-fault sealing integrity, respectively. The first method considers the fault as a thin membrane where permeability depends on the membrane clay mineral content. The method was develop from fault-seal observations in clastic sedimentary sequences under a low differential stress (Knipe in Structural and tectonic modelling and its application to petroleum geology. Elsevier, Stavanger, 1992 for ex.). Empirical relationships are made between the clay mineral content of the sedimentary layers affected by the fault, the fault offset and the fault permeability (deduced from the history matching of pore pressure signals from both fault compartments). The second method considers the fault as a frictional interface, and it calculates the ratio between the stresses normal and tangential to the interface knowing the regional stress regime. This method was developed to describe fault permeability variations in low permeable rocks subject to deep and high differential stresses (Ferrill et al. in Solid Earth 11:899–908, 2020). It relies on observations that fault permeability vary at fault mechanical activation through mechanisms of slip and dilation. The method uses the ratio between stresses to conduct a qualitative estimate of how much the fault figured as an interface tends to dilate under slip, and considers that the higher the tendency to dilate the higher the along-fault permeability should be without giving any quantitative estimate. Second, we discuss how seismicity induced by CO2 storage projects can be considered. Compared to fault seal this is a more recent concern that attracted more attention when seismicity started to be induced by wastewater injections or shale gas hydraulic fracturing, and came the need to better assess the seismic risk related to large scale CO2 injections (Zoback and Gorelick in Proceed Nat Acad Sci 109:10,164–10,168, 2012). Here, we introduce some of the fault physics used in estimating induced seismicity, and how it can be applied to CO2 projects induced seismicity rick assessment. Finally, this first chapter allows us to highlight the complex and multiple fault zone attributes that need to be considered at basin scale to assess fault seal and seismic risk.