The paper presents an overview of the results on turbulent mixing of inert and reacting flows in a co-axial jet mixer at high Reynolds and Schmidt numbers. Flow modes without a recirculation zone (
-mode) and with intense separation and development of a recirculation zone (
-mode) are considered. The study has been performed using numerical (RANS, LES) and experimental methods (LDV, PLIF). Performances of various numerical models to predict passive scalar mixing and reacting flows are discussed. The influence of various parameters on mixing, the structure of a scalar field and its dissipation field, multifractal properties of the dissipation field and isotropy of the scalar field are studied for the case of passive scalar mixing. Concentrations of the neutralisation reaction product and the mixture fraction are measured simultaneously using the PLIF. A few RANS and LES models are validated by comparing with the PLIF measurements. The influence of various parameters on the selectivity of competitive-consecutive reaction is analyzed using the RANS.