This study is designed to meet the following objectives: (1) To study attitude and behavior regarding marriage and age at marriage, (2) To learn correlates of age at marriage and to examine their relations. (3) To measure relative importance of the correlates of age at marriage, and (4) To study relations of age at marriage and family planning practice to fertility and their relative importance as correlates of fertility. The data are obtained by an independent cross-sectional survey in three study areas purposively selected to represent metropolitan, semiurban, rural population. The study population is confined to women age 17-50 as of survey. The overall response rate is 90%. Reliability of data is measured by individual and aggregate inconsistency based upon a 15% subsample of the original interviews. The individual inconsistency (31%) is found to be high compared to the aggregate inconsistency (6%) for all 85 variables. However, the magnitude of differences betwaen means is small, and tha mean absolute shifts and! proportional shifts are also small on the whole. In a word, respondents did not change their answers too extremely or radically. Thec study populations of each study area are compared on some basic characteristics. It is found that the three study populations have more dissimilarities than similarities. The findings on seven different attitudinal positions of women toward marriage indicate that there have been tremendous changes in all study areas from "traditional* attitudes which have been prevalent for a long time in Korean socirty to "liberalized" or "modernized" attitudes. An apparent tendency is that women generally take a position of a "golden mean" attitude by not preferring either extreme of marriage attitudes. Nevertheless, the young, single, educated, and urbanite appears more "liberalized." There has been some increase in ideal age at marrige from 1958 to 1970 for both sexes. No age group, marital status, or study area differentials in ideal age at marrige are found, the average idea) age at marriage in every sub- group being 24-25. Awareness of existing legal marriageable ages is low; only 4.4% are aware that "with parental permission: minimum age for males is 18 years and for females 16 years," and only 3.7% are aware that "without parental permission: 27 years for males and 23 years for females." People in Korea tend to marry spouses who are in various social ways like themselves; the similarities include (a) education, occupational status of father, (c) egonomicc status, (d) usual residence befor marriage, and (e) religion. Both singulate and actual mean ages at marriage in this study confirm the trend of rising age at marrige previously established by other independent studies. The urban-rural differential in age at marriage is observed, but the differentia! narrows down gradually from 1935 to 1970. All socio-economic, demographic, and other variables pertaining to wife before and at first mar riage excluding (a) religion, (b) father's occupation, and (c) age of menarche, are correlated with respondent's age at first marriage, whereas only three variables out of all socio-economic variables relating to husband before and at wife's first marriage, viz.. (a) education, (b) usual residence, and (c) economic level of his old home, are correlated with respondent's age at marriage. Among socio-economic and modernity variables related to either husband or wife at the time of survey, only education and duration of residence are correlated with wife's age at first marriage. Among the correlates of respondent' age at first marriage, education is in general the most important variable. However, it is found that wife's education is more important than husband's. The combined effects of the correlates studied explain no more than about 40% of variance for any of the selected groups of variables. Points which might counteract the effects of late marrige on fertility are not serious in Korea. For each of the correlates of the three fertility indices chosen for this study, namely, (a) number of living children, (b) number of live births, and (c) number of pregnancies, age at marriage is the major contributor to the variance in all age groups except the age group of 20-29 in which the index of family planning practice is the major contributor. The proportion of variability in fertility indices accounted for by the correlates is never more than 40% of the total variance in any age group. Based upon the findings from this study, it could be concluded that in the foreseeable future (a) celibate group will not be increased to a point that would slow down population growth rate in Korea, (b) age at marriage will not increase continually, (c) although education stands out as the major contributing variable which independently explains the variation in age at marrige, it seems probable that education may not be the major variable in the near future, and (d) despite the fact found by this study that age at marriags has bean the major contributor to the variance of each of the fertility indices used, family planning practice will play a more important role in the reduction of fertility in the Korean society. Therefore, factors interrupting practice of family planning must be eliminated and famliy planning program should be strengthened if further fertility reduction is needed.