Burden of proof rules, which require a specified party to produce evid
ence on a contested issue, are central to the adversary system. In thi
s article, we model burden of proof rules as a device for minimizing t
he costs of litigation. The central point to emerge from the model is
that, properly assigned, a burden of proof rule economizes on the tran
smission of information to the court. We use the model to explain char
acteristic practices of courts in assigning the burden of proof.