I analyze the effects of competition on process innovation and product introduction and obtain robust results that hold for a range of market structures and competition modes. It is found that increasing the number of firms tends to decrease cost reduction expenditure per firm, whereas increasing the degree of product substitutability, with or without free entry, increases it—provided that the average demand for product varieties does not shrink. Increasing market size increases cost reduction expenditure per firm and has ambiguous effects on the number of varieties offered, while decreasing the cost of entry increases the number of entrants and varieties but reduces cost reduction expenditure per variety. The results are extended to other measures of competitive pressure and to investment in product quality. The framework and results shed light on empirical strategies to assess the impact of competition on innovation.