Opportunities are options—rights but not obligations to take some action in the future. Capital investments, then, are essentially about options. Over the past several years, economists including ourselves have explored that basic insight and found that thinking of investments as options substantially changes the theory and practice of decision making about capital investment. Traditionally, business schools have taught managers to operate on the premise that investment decisions can be reversed if conditions change or, if they cannot be reversed, that they are now-or-never propositions. But as soon as you begin thinking of investment opportunities as options, the premise changes. Irreversibility, uncertainty, and the choice of timing alter the investment decision in critical ways.