Perspective on “The effect of shape on the interaction of colloidal particles” [Onsager L (1949) Ann NY Acad Sci 51:627]

Onsager’s paper on the effect of shape on the interaction of colloidal particles is seminal in many ways. I shall focus on two aspects: it is (to my knowledge) the earliest classical density functional theory, and it demonstrates the possibility of ordering transitions driven by entropy.