Prior research has supported the development of language through interaction (e.g. Swain, Brooks & Tocalli Beller, 2002; Swain, 2005). Following Sociocultural theory (SCT) notions (Vygotsky, 1978), metatalk (MT) is claimed to be a specific aspect of interaction that leads to language development (e.g. Swain & Lapkin, 2002; Swain, 2005). This study takes a step further to explore the relationship between MT and language development by inquiring specifically about vocabulary development. Learners of Spanish as a second language completed a dictogloss activity and their interactions were recorded, transcribed, and analyzed. The analysis of lexical language-related episodes (LLREs) was carried out by adopting Sociocultural theory as a theoretical framework in order to trace lexical development in interaction through MT. Conclusions indicate that (1) because MT is a cognitive and semiotic tool that enables lexical development by means of participation in socially-mediated activities it is comparable to other forms of speech in their mediation functions and potential; (2) learners’ MT included the analysis of meaning, spelling, pronunciation, and word function, and reflected SCT concepts such as agency, situatedness, and task versus activity that explain their reliance on the word depth knowledge construct; and (3) SCT principles (e.g. roles, regulation) provide a window into learners’ transformation and imminent development during MT. Inferencing strategies and interaction features contribute further details to the analysis of how MT unfolds. New categories describing MT in interaction emerged from the data and illustrate how learners object-regulate and position themselves in the task. These results provide a detailed account of how MT occurs in collaborative settings to mediate vocabulary knowledge. This research contributes to the study of L2 vocabulary learning through the application of SCT. / text