The function of speech and its implications for studying, understanding, and promoting language development are explored in this paper. Function is considered to be the purpose of the speaker when speaking, variously termed context of situation, situation, context, circumstance, or mode. It is noted that very few studies of speech and speech development have looked at the function of speech, but those that have found differences in amount of speech and sophistication of speech depending upon the function. The need to obtain multiple samples of speech for evaluation, including samples of speech used for different purposes, is emphasized. (MKM)