Growth theory offers two plausible explanations of growth. One stresses the supply of productive ideas and holds that the industrial revolution had to wait until we had thought up enough inventions to lift us into the era of modern growth. It says, roughly, that the growth of living standards...

Product-recall data and information on stock-price reactions to recalls are used to estimate the value of reputation in a model in which product quality is not contractible. A recall is the result of a product defect that signals low effort. The recall triggers a reduction in the firm's product...

This paper studies optimal investment policies when the production function depends on capital of various vintages. In such an environment it is natural to ask whether the firm will invest in old-vintage capital at all. In this paper I derive such a condition. Predictably, investment in old...

Aside from the equilibrium that Hotelling (1931) displayed, his model of non-renewable resources also contains a continuum of bubble equilibria. In all the equilibria the price of the resource rises at the rate of interest. In a bubble equilibrium, however, the consumption of the resource peters...

This paper extends Lucas (1978) to a production economy with two capital goods. It is an RBC model in which each unit of investment requires a new idea, an "option". When options are scarce, new capital is harder to put in place and the value of old capital rises. Thus the stock market and...

This paper models the product cycle and explains how it relates to world inequality. In the model, both phenomena arise because skilled people have a comparative advantage in making high-tech products. The model can explain up to a 10:1 income differential between people and up to a 7:1...

Until its sales of a product materialize, a firm is a "pre-producer" in the market for that product. That firm may may be a new start-up, or it may already sell other products. Firms that do not succeed in generating sales eventually become discouraged and move on to other activities. When this...

I estimate a model in which new technology entails random adjustment costs. Rapid adjustments may cause productivity slowdowns. These slowdowns last longer when retooling is costly. The model explains why growth-rate disasters are more likely than miracles, and why volatility of growth relates...

If machines are indivisible, a vintage capital model must give rise to income inequality. If new machines are always better than old ones and if society cannot provide everyone with a new machine all of the time, inequality will result. I explore this mechanism in detail. If technology resides...

In this survey, I discuss four sources of growth of knowledge: research, schooling, learning by doing, and training. In trying to disentangle what is important, I emphasize the following facts: (1) even the most advanced countries spend far more on adoption of existing technologies than on...