This talk presents ongoing computational modeling research to predict the structural, electronic, magnetic, thermodynamic, and elastic properties of single-phase high-entropy alloys (HEAs) with the FCC, BCC and HCP structures. The techniques used include: Empirical thermo-physical parameter calculations, CALPHAD method, first-principles density functional theory (DFT), Monte Carlo (MC), and molecular dynamics (MD) simulations. The criteria to identify single-phase HEAs are reviewed. The atomic structures (including the lattice distortion) of example solid solution HEAs are evaluated with respect to the crystal structures and compositions. Their entropy and enthalpy sources (e.g., configurational, vibrational, and electronic entropies) as a function of temperature are calculated using DFT, MC and MD methods, and the results are compared with the predictions obtained from CALPHAD modeling. The elastic constants, the polycrystalline bulk and shear moduli, and solid solution strengthening effects of single-phase HEAs are predicted. The predicted elastic properties are compared with experiments where available.