CO2 injection into subsurface geological formations induces changes in the state of the system, as characterised by local pressure and saturation changes. Being able to understand, predict, monitor and manage such changes is critical to the successful development of carbon capture and storage (CCS) projects. Key to this is the ability to model injectivity, migration and trapping of CO2. While injectivity can be understood using analytical models, migration and trapping calculations are generally carried out using numerical codes. A good understanding of the various trapping mechanisms can assist with developing engineering options to maximise storage capacity and security. The financial viability of CCS projects may be enhanced by consideration of CO2-enhanced oil recovery (EOR).