Growth and development of the King Rail (Rallus elegans) from hatching to first flight were studied by observations and measurements of captive birds and by observations of natural nests in the field. This is the fourth in a series of reports on the life history of the King Rail (Meanley 1953, 1956, and 1957). Information in this paper is intended to supplement the data of Bent (1925) on growth and development and the description of juvenal plumage given by Friedmann (1941).