The ultimate composition of the CO2 stream captured from fossil fuel power plants or other CO2 intensive industries and transported to a storage site using high pressure pipelines will be governed by safety, environmental and economic considerations. So far, most of the studies performed on this topic have been limited in scope, primarily focusing on investigating the impact of the CO2 stream impurities on each part of the Carbon Capture and Sequestration (CCS) chain in isolation. This is a significant drawback given the markedly different sensitivities of the pipeline, well bore materials and storage sites to the various impurities. For example, given the risk of water table contamination, trace elements such as Lead, Mercury and Arsenic in the CO2 stream are of far greater concern in an aquifer storage site than compared to the pipeline. On the other hand, even small concentrations of water in the CO2 stream are detrimental to the pipeline due to corrosion, but of benefit even at high concentrations during storage given the immobilisation effect of water on CO2. 'What is good for the pipeline is not necessarily good for storage'. It is clear that the optimum composition and concentration of the impurities in the captured CO2 stream involves a delicate balance between the different requirements within the CCS chain, spanning capture, transportation and storage, with cost and safety implications being the over-arching factor. Pivotal to these considerations is an understanding of the impact of the impurities on the physico-chemical properties of CO2 and its hazard profile. This paper presents and overview of the current FP7 European Commission CO2QUEST project involving the collaboration of 12 industry and academic partners in Europe, China and Canada aimed at addressing fundamentally important and urgent issues regarding the impact of the typical CO2 streams impurities captured from fossil fuel power plants on its safe and economic transportation and storage. The work programme, spanning 36 months, focuses on the development of state-of-the-art mathematical models, backed, by laboratory and industrial-scale experimentation using unique EC-funded test facilities to perform a comprehensive techno-economic, risk-based assessment of the impact of the CO2 stream impurities on the phase behaviour and the physico-chemical reactions governing the pipeline and storage site integrities. The above involves the determination of the important CO2 mixtures that have the most profound impact upon the pipeline pressure drop, compressor power requirements, pipeline propensity to ductile and brittle facture propagation, corrosion of the pipeline and well bore materials, geochemical interactions within the well bore and storage site, and the ensuing health and environmental hazards. Based on a cost/benefit analysis and whole system approach, the results will in turn be used to provide recommendations for tolerance levels, mixing protocols and control measures for pipeline networks and storage infrastructure thus contributing to the development of relevant standards for the safe design and operation of CCS. Acknowledgement: The CO2QUEST project has received funding from the European Union 7th Framework Programme FP7-ENERGY-2012-1-2STAGE under grant agreement number 309102.