A description is presented of all the thermo- and hydrodynamic, high-frequency, kinetic, and magnetic properties of $^3$He--$^4$He solutions. The treatment does not resort to any model representations on the nature of the interaction of the 3He quasiparticles. It is based on the fact that an expansion in terms of the interaction for a solution at low temperatures formally coincides with an expansion in terms of the 3He concentration. All of the experimental data on the low-temperature properties of the solution known to us and analyzed in this study agree well with the presented theory up to the very greatest concentrations. An entire set of new phenomena is predicted, among which the most striking are the magnetokinetic effects--an enormous increase in the kinetic coefficients upon magnetizing the solution. The transition of $^3$He in solution to the superfluid state is discussed. Detection of this effect is apparently possible even now.