First words have been the subject of serious attention for more than 200 years, ever since a few scientists and other parents began to keep diaries of their babies' words in the 18th century. We still study the classic diaries; researcher-parents continue to keep diaries; and researchers even train parents in how to keep diaries so they may study the early words of larger numbers of children. More objective observations of infants under controlled conditions also yield information about how children acquire a vocabulary of words in their second year. And now diary and observational studies are supplemented by experimental studies in which researchers teach words to 1- and 2-year-olds.

Two hundred years later, what do we know about First Words and the development of early vocabularies? Certain landmarks in the literature can point the way in answering that question. The summary chapters by Dorothea McCarthy in 1946 and 1954 are a good place to start. They provide a wealth of material from studies that had accumulated at each time. The study Infant Speech published by M. M. Lewis in 1936 is a source of many theoretical and empirical observations of early language that continue to reverberate in research today. The diary study that stands out for both the breadth of its coverage and the depth of its insights is in the four volumes published by Werner Leopold between 1939 and 1949.