In a first survey of its type, we measure development and modification of consumer products by product users in a representative sample of 1,173 UK consumers age 18 and older. We estimate this previously unmeasured type of household sector innovation to be quite large: 6.1% of UK consumers¿nearly 2.9 million individuals¿have engaged in consumer product innovation during the prior three years. In aggregate, consumers' annual product development expenditures are more than 1.4 times larger than the annual consumer product R&D expenditures of all firms in the United Kingdom combined. Consumers engage in many small projects that seem complementary to the innovation efforts of incumbent producers. Consumer innovators very seldom protect their innovations via intellectual property, and 17% diffuse to others. These results imply that, at the country level, productivity studies yield inflated effect sizes for producer innovation in consumer goods. They also imply that existing companies should reconfigure their product development systems to find and build on prototypes developed by consumers.