The contribution that x‐ray diffraction has made to the understanding of triglyceride polymorphism is reviewed. The crystal structure of these compounds is explained in terms of molecular orientation in the crystal lattices. At the present time only the crystal structure of the monoacid saturated triglycerides has been reasonably well defined. Mixed triglycerides and mixtures thereof have not yet been fully investigated. This review stresses the need for systematic correlation of the crystal structure of fats with the molecular composition and configuration.