The goal of this study was to find out how, in young children, conversations with an adult contribute to establishing a shared expression of beliefs through assertive speech acts. Children age 22 months were observed in a picture-book situation with their mother. On the basis of work on early semantic relations, 3 categories of assertives were considered: (a) assertives related to existence, presence, absence, and recurrence; (b) assertives related to action; and (c) assertives related to locative action, attribution, locative state, state, and possession. The results show how mothers contribute to the elaboration of assertives, particularly the ones that might seem more cognitively and linguistically difficult for 22-month-old children. Assertives in the existence category were produced mostly in 1 speech turn and without maternal support. In contrast, assertives of state, possession, and so on, are the most frequently produced in 2 speech turns and with maternal support. When interdiscursive links in mother-child dialogues were taken into account, evidence of some transitional phenomena in the step-by-step, joint elaboration of assertive acts was found.