Previous research on American Sign Language, while analyzing the complexity and systematicity of the language from the phonological to the syntactic levels, has overlooked the area of grammaticalization studies as a means of accounting for the current shape of the language. The present study examines the process of grammaticalization in ASL, verifying its presence in the language, appealing to its basic principles (in cooperation with those of internal reconstruction) as a justification for certain structural properties of the language, and drawing parallels between the various stages represented in the ASL data and those found in oral language. The more advanced stages of grammaticalization (i.e. those situations involving fusion and affecting the language's syntax) are examined in-depth, leading to the proposal of a `temporal-ordering' analysis (i.e. Mithun, 1997) to explain the sequencing of verbal morphology in ASL where other theories––such as Bybee's (i.e. 1985, 1994) relevance hypothesis––are unable to account for the present shape of the verbal complex.