The present paper is based on field surveys of two locations of rural West Bengal during the1990s. It presents contrasting scenarios of fertility behaviour and its transition for one individual tribe (namely Santals) between the two locations as well as for lower caste people in one region. The study reveals that the Santals, who migrate seasonally, evince not only low fertility but they also appear far ahead in terms of contraceptive practices and fertility transition as compared to their tribal counterparts in a location from where Santals do not migrate. In fact the seasonally migrant Santals appear more motivated and mature users of contraceptives (e.g. oral pills and condoms) than even the non-migrant lower caste (nontribal) people, who, though they have undergone mass sterilisation, could not achieve as low as the fertility of seasonally migrant Santals. The positive roles of seasonal migration (e.g. through augmenting incomes and aspirations as well as social interactions and diffusion of knowledge, ideas and motivation relating to family planning) in hastening fertility transition have thus been the central message of the present study. Although all possible encouragement and support for augmentation of seasonal migration and mobility (e.g. development of transport network and provisions for schooling of children of migrant households) seems to be the immediate policy prescription from our study, this should by no means be construed as alternatives to the longer term programmes for permanent and balanced development of the backward regions from where people need to migrate seasonally.