We study how intra-industry product diversity affects firm performance by analyzing the implications of expanding a firm's product line within its core business. We conjecture that increases in product diversity initially undermine performance because of negative transfer effects but then improve it due to economies of scope. We further theorize that this U-shaped effect of product diversity becomes more pronounced as the firm increases the intensity of its technology investment, yet is likely to be attenuated by the firm's accumulated experience with intra-industry diversification. Data on 156 U.S.-based software firms operating from 1990 to 2001 furnish support for these conjectures. Our study advances emerging research on intra-industry diversification by underscoring some of its contingent performance effects. Copyright © 2013 John Wiley & Sons, Ltd.