We review the properties of simple diatomic molecular glasses as explored by nuclear magnetic resonance techniques and measurements of the dielectric susceptibility. <...> We focus on the behavior of classical molecular rotors formed by solid N2—Ar mixtures and discuss the time dependent behavior in terms of replica symmetry breaking theories. <...> INTRODUCTION Understanding the underlying physics of glass systems remains a major challenge for contemporary condensed matter physics. <...> Of all the different types of glasses: fragile glasses [ 1 ], spin glasses [ 2 ], orientational glasses [ 3—6], and quadrupolar glasses [ 7, 8 ], the simple molecular glasses [ 9 ] provide a particularly straightforward case where the characteristic glass features of frustration and disorder can be formulated clearly and realized experimentally without ambiguity. <...> In this review we will discuss the properties of molecular glasses formed by solid mixtures of diatomic molecules and isoelectronic diluents, and in particular solid ortho-para H2 and solid N2—Ar alloys and analyze the characteristic hysteresis in terms of a generalized fluctuation-dissipation theorem introduced by Cugliandolo and Kurchan [ 10 ]. <...> Long-range orientational ordering of the molecular axes of pure diatomic molecular solids occur in several cases — ortho-H2, N2, O2 … at low temperatures. <...> Note that for hydrogen the orbital angular momentum J is a good quantum number with J = 1 for ortho-H2 molecules at low temperatures and J = 0 for spherical para-H2 molecules. <...> Ortho-H2 and N2 molecules possess an electric quadrupole moment as well as an interatomic axis both of which are free to fluctuate with respect to the molecules fixed center of mass in the lattice structure at high temperatures. <...> At low temperatures, however, the anisotropic electrostatic interactions (mainly quadrupole-quadrupole) between the molecules become significant and the axes of the molecules orient parallel to specific crystalline axes to lower the total free energy. <...> In the case of solid H2 and solid N2 the gain in energy is sufficient to generate a lattice change from h.c.p. to f.c.c. The final long-range ordered structure is a Pa3 structure consisting of four interpenetrating simple cubic sub-lattices with the molecular alignments parallel to a given body diagonal of one of the sub-lattices. <...> Each number designates molecules with the same alignment axis parallel to one of the four body diagonals <...>