CO2 conversion to produce useful fuels/chemicals is a promising route for reducing CO2 emission as well as for exploring the promising energy storage method. To facilitate the research and development of CO2 conversion, this paper provides a comprehensive overview of CO2 conversions using advanced materials/nanomaterials and technologies for the production of useful fuels/chemicals. The molecular structure, thermodynamics and kinetics of CO2 are reviewed for the understanding of fundamentals and explaining why C=O double bonds are difficult to break. The mechanisms and features of various conversion technologies are summarized and classified into enzymatic, mineralization, photochemical/photo-electrochemical, thermochemical as well as electrochemical processes. In particular, by comparing electrochemical conversion technologies at low and high temperatures, CO2 conversion at intermediate temperatures is emphasized. Furthermore, the economic feasibility for CO2 utilization is analyzed with cases for the production of various chemicals/fuels. The technical and application challenges of CO2 conversion into useful fuels/chemicals are also summarized, composing mainly of: insufficient fundamental understanding, low product selectivity, as well as low efficiency and stability. To overcome these challenges, future research directions are proposed in this review.