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Poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) crystallize into a stereocomplex with a melting point 50 °C higher than the crystals of the enantiomers. The racemic crystal is formed by packing β-form 3₁-helices of opposite absolute configuration alternatingly side by side. Single crystals of the stereocomplex exhibit triangular shape. The drastic difference of the powder patterns evidences the different packing of the β-form in the stereocomplex and in crystals of the pure lactides. By force field simulation of the stereocomplex and the PLLA unit cells and of their powder patterns, the reasons for the different packing could be clarified. Between the β-helices in the stereocomplex, van der Waals forces cause a specific energetic interaction-driven packing and, consequently, higher melting point. Helices of identical absolute configuration pack different from pairs of enantiomer β-helices. Packing favors α-type helication. A …