This Special Issue presents 16 papers selected from IX-th International Conference on Computational Heat and Mass Transfer (ICCHMT2016) held in Cracow, Poland, 23-26 May 2016. The Conference Topics included: Discrete methods, Lattice Boltzmann method, Molecular dynamics simulations, Monte Carlo method, Cellular automata, Recent developments on Navier-Stokes equations solvers, Validation of computational methods, Multi-phases, gas-liquid, liquid-solid, etc.; Solidification and melting, Complex chemical reaction modelling, Reactive flows and combustion, Internal flow and heat transfer, Double-diffusive convection, Porous Media Heat Transfer, Heat Exchangers, Steam and Gas Turbines and other relevant topics related to computational heat and mass transfer. Selected peer-reviewed papers related to the numerical modelling of heat and fluid flow processes were selected for publication in this Special Issue of International Journal of Numerical Methods for Heat and Fluid Flow.