The rising number of multi-earner families has been one of the most important socioeconomic developments of the 1970s; since 1970, the number of such families has increased by more than 3 million. Almost exclusively responsible for the rising number of multi-earner families have been the steep annual increases in the number and proportion of working wives. Since 1970, the number of wives in the work force has increased by one-third (to nearly 24 million). Many of the working wives were also working mothers, since 16.6 million or 54 percent of the women with children under 18 were working; 79 percent of divorced mothers worked in March 1979. Among the most striking changes that occurred during the 1970s was the sharp rise in the number of working women heading one-parent families (one of seven families in 1979). Tables in this report contain data on workers by race, sex, age, marital status, Hispanic origin, presence and age of children, number of wage-earners in family, contributions of wife's earnings, family income, single-parent family income, occupation, and full- or part-time employment. (KC)