This paper discusses the role of attention to uncertainty in mediating the transition from sensorimotor activity to language. It is proposed that language from the very beginning is used to resolve uncertainty by selectively marking points of change, deviation from the familiar or choice from among alternatives. Several research findings are summarized in order to support this proposal: (1) Young children selectively give linguistic mention to the variable element in both linguistic and non-linguistic sequences of behavior, whether it be mention of object, persons, or actions. (2) Young children's natural speech rarely includes mention of an agent, except in cases involving uncertainty. The agent seems to drop to background awareness if it is an invariant feature of the situation. (3) The uncertainty which young children orient to cannot be equated with the concept of importance or an absolute concept of salience. Entities that are most important to the child (self, mother) under normal circumstances recede to background awareness because they are taken for granted. The child orients to changes in states, and it is these which are expressed in speech. (4) The use of words to mark change or to partition alternatives holds across a wide range of semantic functions. Just as novelty is encoded in early development in response to visually or enactively presented situations, in later development novelty is encoded in response to linguistic situations. (Author/SS)