The object of the paper is to elucidate the injection, atomization and mixing processes in high-pressure liquid rocket engines. Theoretical studies of coaxial spray generation, single injector experiments under ambient and elevated pressure conditions using simulation fluids and the attempt to model the atomization process are described. The most important fluid mechanical processes leading to coaxial atomization and mixing as turbu-lence in the liquid jet, surface instability, surface wave growth, droplet detachment (primary break-up), droplet break-up (secondary break-up), evaporation and dispersion are identified and investigated. In the proposed atomization model, sub-models for the liquid break-up and droplet flow are solved in conjunction with the calculation of mean flow properties of gas and liquid flow. The model has been applied to various injection conditions and the simulation results are compared with experimental data.