The purpose of this study was to determine the extent to which preschoolers have acquired some of the rules governing politeness when they interrupt conversations. (An interruption was defined as an utterance by a child to two or more people who were already engaged in conversation, and where the topic of the child utterance was unrelated to the ongoing conversational topic.) Eighteen 3- to 5-year-old boys and girls were observed in their classroom while interacting with one another. Observations yielded instances of children's attempts to enter ongoing conversations between child/child, adult/child, and adult/adult pairs. Results indicated that preschoolers rarely used polite strategies (e.g., waiting for acknowledgement) or verbal politeness formulas (e.g., "Excuse me") before interrupting. Adult/child pairs were more frequently interrupted than were adult/adult or child/child pairs. Older children and girls tended to interrupt at a closer distance to those they were interrupting than did younger children and boys. The results are discussed in terms of the development of the sociolinguistic rules and cognitive abilities involved in entering ongoing conversations. (Author/MP)