The present invention relates to crystalline polymorphic forms of monosodium N-[8-(2-hydroxybenzoyl)amino] caprylate ("SNAC"), including two hydrates, a methanol solvate, and an ethanol solvate, of SNAC. More specifically, the present invention provide six polymorphic forms of SNAC (hereafter referred to as Forms l-Vl). The present invention also provides an amorphous form of SNAC.