The objective of reservoir engineering is to gain an understanding of the static and the dynamic behaviours of the reservoir and to optimize hydrocarbon production. Reservoir characterization can be viewed as providing the static 3-D mapping of rock and fluid parameters. Reservoir monitoring involves assessing the dynamics of the fluid flow as a function of time. Production geophysics addresses these two issues by providing: (1) valuable images of the major geological features of the reservoir and their spatial organisation; (2) quantitative physical parameters that can be related to rock and fluid properties via petrophysics; and (3) repeated (time-lapse) images that can be representative of the reservoir dynamics. All the geophysical techniques, including DC electrical techniques, electromagnetics methods (GREAVES ef al., 1991), and gravity are currently used in reservoir characterization. In this article, however, we deal with the seismic methods only. First we recall what information about the earth＇s interior a seismic experiment can provide; then we deduce what the reservoir model and the seismic data should ideally have in common and what is presently achieved in practice. Next we consider the present usage of seismics in the building of the reservoir model, and what the more advanced techniques can offer at present and in the future. We conclude by assessing the possibilities and limits oi reservoir monitoring by seismics.