This article discusses trends in the occurrence of out-of-wedlock births and factors which contribute to or are associated with illegitimate pregnancies. Specifically discussed are the rates of increase of such births, particularly among unmarried teenage mothers, and the ethnic, social, and psychological characteristics of unwed mothers. It is felt that the rise in illegitimacy is "substantial but not alarming" and that out-of-wedlock births are related both to socioeconomic and racial factors, but that socioeconomic factors are probably more significant. (LB)