The policy world is awash with worries about spectrum shortages as demand for wireless services grows. Using data on more than 69,000 licenses from every FCC spectrum auction since 1996, this paper disentangles and quantifies major factors that differently contribute to license value. I find that, all else equal, flexible use licenses are significantly more valuable than licenses that proscribe certain uses, policy uncertainty depresses license value, and Verizon and AT&T pay more than other carriers for licenses. I also find that larger geographic definitions generally correlate with lower license values and, contrary to conventional wisdom, more bandwidth is not correlated with higher values. Finally, using auction data and information from large secondary trades, I find that spectrum prices have been increasing since the mid-2000s, though some evidence suggests that the rate of increase has been slowing.