The technologies for CO2 capture and storage (CCS) differ much in design, operation conditions, and the amount and nature of impurities in the captured CO2. The presence of impurities affects the thermophysical properties of CO2 significantly. In particular, properties such as phase equilibrium behavior, density, viscosity, thermal conductivity, and diffusion coefficient are much affected. The development and technical breakthrough of new CCS technology rely on a deeper understanding of the thermophysical properties of CO2 mixtures. In this chapter, the available experimental data and theoretical models about the thermodynamic and transport properties of mixtures at conditions relevant to CCS have been summarized. Knowledge gaps have been identified; in particular, more measurements are needed to close the experimental gaps. In addition, the impacts of impurities on operation of different CCS processes have been discussed, including CO2 conditioning, compression, liquefaction, transport, and storage. Recommended levels of impurities from different sources have been reviewed and compared.