In this article, the authors explore the origins and evolution of product markets from a sociocognitive perspective. Product markets are defined as socially constructed knowledge structures (Le., product conceptual systems) that are shared among producers and consumers-sharing that enables consumers and producers to interact in the market. The fundamental thesis is that product markets are neither imposed nor orchestrated by producers or consumers but evolve from producer--eonsumer interaction feedback effects. Starting as unstable, incomplete, and disjointed conceptual systems held by market actors-which is revealed by the cacophony of uses, claims, and product standards that characterize emerging product markets-product markets become coherent as a result of consumers and producers making sense of each other's behaviors. The authors further argue that the sensemaking process is revealed in the stories that consumers and producers tell each other in published media, such as industry newspapers and consumer magazines, which the authors use as data sources. Specific hypotheses pertaining to the use of product category labels in published sources and the acceptability of different product category members throughout the development process are tested for the minivan market between 1982 and 1988. The findings suggest that category stabilization causes significant differences between consumers and producers in how they use product category labels for emerging and preexisting categories. The findings also show that, as stabilization occurs around a category prototype, the acceptability of particular models changes without any physical changes to the models. T he notion of "product markets" is fundamental to marketing theory. Product markets are regarded as the meeting grounds for buyers and sellers of goods (e.g., Robinson 1933). They are the bounded arenas in which prices and quantities for substitutable goods and services are negotiated by consumers and producers and are separated from other bounded arenas by gaps in demand between the product groupings. Considerable attention has been given to product market structure and the boundaries between product categories from cognitivist (e.g., Day and Negundadi 1994; Wedel and Steenkamp 1991*) and organizational (e.g., Myers and Tauber 1977*;Porter 1980) perspectives. Research also has attended to consumer and producer roles in defining product market structure (e.g., Day, Shocker, and Srivastava 1979;Ratneshwar and Shocker 1991) and the dynamic forces at play within product market boundaries (e.g., Dickson 1992). The study of product markets remains important as the marketing field ponders questions such as how markets function and evolve, whether market bound-*Authors were limited in the number of references used in text, therefore, those references marked with an * are available at www.