Reproductive development of plants is highly vulnerable to water deficit. Stress early during this phase can delay or completely inhibit flowering, both through an inhibition of floral induction and development. The stage of meiosis is perhaps the most stress-sensitive period of reproduction in all species studied. A meiotic-stage water deficit causes pollen sterility, but usually affects female fertility only under extreme stress. Sterility occurs even though the reproductive structures of stressed plants maintain a high water status, indicating that the response is probably mediated by a sporocidal signal from elsewhere in the plant. Rice and maize plants are also highly vulnerable during flowering (anthesis) and early grain initiation. Stress during this period can cause loss of pollen fertility, failure of pollination, spikelet death, or zygotic abortion. Changes in carbohydrate availability and metabolism appear to be involved in the effects of stress during meiosis and anthesis. Stress during early grain development curtails the kernel sink potential by reducing the number of endosperm cells and amyloplasts formed. Controls underlying these effects are poorly understood, although hormones may be involved. A water deficit during any stage of grain development causes the premature cessation of grain filling. Kernel moisture content and its direct impact on metabolism appear to be key regulatory factors in shortening the duration of grain filling.