I study ﬁrm behavior in new markets by examining coal-dependent private electric utili-ties’ beliefs about the sulfur dioxide allowance price following the implementation of the U.S. Acid Rain Program. The program is the ﬁrst large-scale cap-and-trade program, exposing the electric utility industry to a wholly novel market for pollution allowances. I estimate ﬁrms’ beliefs about the allowance price from 1995 to 2003 using a ﬁrm-level dynamic model of allowance trades, coal quality, and emission reduction investment. I ﬁnd that ﬁrms ini-tially underestimate the role of market fundamentals as a driver of allowance prices, but over time their beliefs appear to converge toward the stochastic process of allowance prices. Such beliefs in the ﬁrst ﬁve years of the program cost ﬁrms around 10% of their proﬁts. Beliefs also change the relative eﬃciency of cap-and-trade programs and emission taxes.