Mutual exclusivity is a word learning constraint in which the learner assumes that a given word refers to only one category of objects. In spoken languages, mutual exclusivity has been demonstrated in monolingual children as young as 17 months and cross-linguistically, while multilingual learners show an attenuated mutual exclusivity bias. Mutual exclusivity has not been robustly demonstrated in deaf children acquiring American Sign Language (ASL). Further, it is unclear if mutual exclusivity applies to those learning both a signed and a spoken language. Like unimodal bilinguals, bimodal bilingual (BiBi) children learn two words for an object, but these words are separated by modality. A BiBi child could therefore assume that all objects have two words (like unimodal bilinguals) or that all objects have one spoken word and one sign (within-modality mutual exclusivity). The goals of the current study are to demonstrate mutual exclusivity in monolingual deaf children acquiring ASL, and to determine if BiBi deaf children utilize mutual exclusivity within each modality.