Sign language phonology is the abstract grammatical component where primitive structural units are combined to create an infinite number of meaningful utterances. Although the notion of phonology is traditionally based on sound systems, phonology also includes the equivalent component of the grammar in sign languages, because it is tied to the grammatical organization, and not to particular content. This definition of phonology helps us see that the term covers all phenomena organized by constituents such as the syllable, the phonological word, and the higher-level prosodic units, as well as the structural primitives such as features, timing units, and autosegmental tiers, and it does not matter if the content is vocal or manual. Therefore, the units of sign language phonology and their phonotactics provide opportunities to observe the interaction between phonology and other components of the grammar in a different communication channel, or modality. This comparison allows us to better understand how the modality of a language influences its phonological system.