At its core, word learning and recognition concerns a relation between a low-level acoustic signal and a high-level semantic representation. Fundamental to the study of the early lexical-semantic system is the manner and degree to which the acoustic signal activates the semantic representation, and how meanings associated with words relate to one another. An implicit notion in the developmental literature is that upon hearing a word, young children activate the corresponding semantic representation in a dichotomous fashion – i.e., the semantic representation is either activated resulting in word recognition or not activated resulting in lack of recognition. Further, it is not entirely known the degree to which very young children appreciate that word referents are meaningfully related. To date, models of early auditory-semantic processing are primarily based on studies of meaningful relations between words and referents. However, lexical information (i.e., words) is not the only type of auditory input that is meaningful – environmental sounds (e.g., dog barking or pen scribbling) are nonverbal yet complex sounds that carry deep semantic associations with a corresponding referent. Therefore, a thorough investigation into the fundamental relation between acoustic signals and meaning requires an understanding of how meaning is associated with both lexical and non-lexical sounds. A series of four studies with toddlers and adults are presented to investigate three related issues in the study of early auditory-semantic development: 1.) Is lexical knowledge dichotomous or continuous? 2.) How is lexical information semantically processed and organized? 3.) To what degree is such processing specific to language? In the first set of studies, Chapters 2 and 3 present behavioral evidence that early word recognition is not binary, but instead graded, and partial knowledge plays a role in future learning. In the second set of studies, Chapters 4 and 5 replicate and extend findings that suggest the lexical-semantic system is organized as an interconnected semantic network both early in life and into adulthood. Further, these chapters present evidence that the electrophysiological markers of semantic processing are present during environmental sound processing in toddlers and adults, however words and environmental sounds appear to be organized somewhat differently, with a more consistent fine-grained structure for words compared to environmental sounds. Together, these studies provide behavioral and electrophysiological evidence to further our understanding of the nature of the early auditory-semantic system.