Most of our efforts as oil and gas geoscientists are directed toward estimating the earth model. In addition, most of our earth-model estimation involves inversion of one kind or another, even if we don't think explicitly in terms of inversion. When we specialize to seismic, as all seven articles in this special section do, “Imaging/inversion: Estimating the earth model” describes our work. Seismic is a big field, however, and we have not always regarded it as being so unified. After all, what could topics as different as (for example) seismic imaging of structural targets and estimation of reservoir properties possibly have in common? As it turns out, the answer is “plenty,” and our realization of this fact has helped us get better at our jobs; our structural images benefit from knowledge of rock and reservoir properties, and our rock-property estimates improve when we use information from seismic imaging. So the historic concept of a “seismic chain,” whose separate links are acquisition, preprocessing, imaging, inversion, and interpretation, is gradually breaking down as we realize how each step quantitatively influences all the others. In fact, as some of the articles in this section illustrate, the sequential chain is being replaced by a more sophisticated set of feedback loops where the derived information may be used to improve the final result.