Senators John Kerry (D-MA) and Joe Lieberman (I-CT) introduced a climate bill yesterday that, among other things, establishes a cap-and-trade program for greenhouse gases. The virtue of a cap-and-trade program is that it establishes a market price for a pollutant and allows flexibility within and across regulated entities in how to reduce emissions. But any cap-and-trade program must decide whether to allocate the pollution allowances for free or through a government auction, as well as how to distribute both the allowances and any auction revenue.