CO2-rock wettability is a key factor which strongly influences CO2 containment security and storage capacity in the context of CO2 geo-sequestration projects. It is thus vital to understand this parameter in detail. Here the variation of CO2-rock wettability will be demonstrated, and underlying mechanisms will be discussed. Clearly, rock surface chemistry is the prime factor which determines CO2 wettability, while pressure, temperature and brine salinity also play a significant role. Finally, the impact of CO2-wettability at larger (reservoir) scale is illustrated. This talk will thus improve the understanding of a fundamental technical parameter and aid in the larger-scale implementation of CO2 geo-storage schemes.