Fertility has often seemed to be too high or too low, relative not only to social and economic goals, but also to reproductive preferences. In developing countries actual fertility has often been higher than desired family size, while in developed societies fertility tends to be below replacement level even though people generally say that they want at least two children. In explanations of fertility extremes, or of the discrepancies between desired and actual fertility, the effect of partners' holding different preferences has tended to be overlooked. Individual preferences expected to lead to replacement-level reproduction may in combination generate substantially higher or lower fertility. In explaining such outcomes, a crucial question is what happens when spousal preferences diverge. Given that personal practices or social norms may systematically favor high or low preferences in the event of disagreement, chance alone will ensure that desired and actual fertility do not coincide.