Mechanism design theory is used to characterize the properties of a least-cost CRP. If marginal land rents decrease with acres farmed then a least-cost CRP is a set of nonlinear price schedules. If marginal land rents are independent of acres farmed then an offer system constitutes a least-cost CRP. The least-cost offer system gives a useful estimate of the upper bound of a least-cost CRP. Empirical results suggest that a 34-million-acre CRP should have cost no more than $1 billion per year.