Many cases of allomorphic alternation are restricted to specific lexical items but at the same time show a regular phonological distribution. Standard approaches cannot deal with these cases because they must either resort to diacritic features or list regular phonological contexts as idiosyncratic. These problems can be overcome if we assume that allomorphs are lexically organized as a partially ordered set. If no ordering is established, allomorphic choice is determined by the phonology—in particular, by the emergence of the unmarked (TETU). In other cases, TETU effects are insufficient, and lexical ordering determines the preference for dominant allomorphs.