People express their value for a good when they pay something for it. Interpreting good and payment very broadly, we offer a general analytical framework for characterizing such transactions. This framework is suitable for interpreting actual transactions as well as for creating hypothetical transactions for research purposes. It is described here both in general terms and with special application to one particular kind of transaction, contingent valuation studies in which individuals estimate the value of possible changes in atmospheric visibility. In these transactions, as in many others, risk (of undesired changes in visibility) is one principal feature; at least some uncertainty often surrounds other transaction features as well (For example: How much will visibility really change ifI promise to pay for it? Will I really have to pay?). The framework presented here conceptualizes any transaction as involving (a) a good, (b) a payment, and (c) a social context within which the transaction is conducted. Each of these aspects in turn has a variety of features that might and in some cases should affect evaluations. For each such feature, the framework considers first the meaning of alternative specifications and then the difficulties of ensuring that they are understood and evaluated properly. As a whole, the framework provides an integrated approach to designing evaluation studies and interpreting their results.Finding out what something is worth to people is easiest when they engage in observable transactions involving it. Thus, the value of a consumer item is related to how much money people pay to acquire it. The value of a recreational experience is revealed, in part, by the amount of time people spend on it. The value of a political cause is, to some extent, reflected in the energies that people expend pursuing it--getting, in return, either the goal itself or the satisfaction of knowing they at least tried to obtain it. In all such overt transactions, latent predispositions are revealed in concrete actions.People may reveal the value to themselves of a particular thing in a variety of