In this study we examine first use of mode rn contraception in four Gambian villages over 25 years. This is the first such st udy showing micro-level change over time from the first availability of this new technol ogical innovation. In 1975, a medical centre was opened in one village providing contracep tive services free of charge to those who wished to use it. We examined dete rminants of women’s age at first use of modern contraceptives, from 1975 or from age 15 if younger than that in 1975. The ideal of large family size re mains strong, and those at low parity are significantly less likely to start using contraception than those at high parity for their age. Wealth was also significantly related to the probability of contraceptive use, but negatively, with the wealthiest ranked women being the least li kely to adopt the innovation. But we find that the largest effects on the probab ility of uptake were village and calendar year. Over the last 25 years, there is a doubling time of about 10 years in the risk of progressing to first use of contraception. Villages with strong social ties proceed at a similar rate, whereas one vill age that had fewer social tie s with the others proceeded at a much faster rate. Thes e patterns of uptake suggest that cultural transmission has an important effect on the spread of this technological innovation. We also compare the reproductive success (i.e. completed fertility ) of users and non-users, and find that women using contraception actually have higher reproductive success than those that do not. The dynamics of uptake are discussed in the light of both evolutionary and social network models of cultural diffusion.