To reduce infant mortality through improved family planning, a better understanding of the factors driving contraceptive use and how this decision affects infant survival is needed. Using dynamic panel-data models of infant deaths, birth intervals, and contraceptive use, this study analyzes the causal effects of birth spacing on subsequent infant mortality and of infant mortality on the use of contraceptives and the length of the next birth interval. Data are drawn from the Health and Demographic Surveillance System in Matlab, Bangladesh, where almost 32,000 births have been observed from 1982 to 2005. Our main finding is that complete contraceptive use could reduce infant mortality of birth order two and higher by 7.9 percent. The net effect of complete contraceptive use on the total infant mortality rate is small (2.9 percent), however, because the favorable effect on higher order births is partly offset by the rise in the proportion of high-risk first births.