Many biologically important molecules exist as enantiomers. In this chapter the enthalpies of mixing (Hm) of binary mixtures of liquid enantiomers and solid enantiomers in polar and non-polar solvents are discussed in an attempt to understand the molecular interactions between heterochiral enantiomers. The Hm values were very small. The enthalpies of mixing of ternary systems showed unique behavior. The Hm's were exothermic in dilute solutions of an enantiomer but this exothermicity decreased with increasing concentration of an enantiomer. To evaluate molecular interactions in solvents, ab initio quantum chemical methods were adopted.