This paper presents a formalization of the common structure underlying different proposals concerning the geometry of phonological features. Using the concepts and tools of elementary set theory, lattice theory, and the theory of independent Boolean algebras, ametatheory of autosegmental feature structure is developed. This metatheory enables us to compare contemporary autosegmental phonology to the now abandoned “standard” phonology and to the historically important Pānini-type phonology as well, and to investigate the restrictions on the use of features in phonological theory.