There has been a systematic decline in the number of publicly-traded firms over the last two decades. Half of the U.S. industries lost over 50% of their publicly traded peers. The decline has increased industry concentration, as the void left by public firms has not been filled by an increase in the number of private businesses or by greater presence of foreign firms. Firms in industries with the largest decline in the number of firms have generated higher profit margins and abnormal stock returns, and enjoyed better investment opportunities through M&A deals. Overall, our findings suggest that the nature of US product markets has undergone a structural shift that has potentially weakened competition.