In this paper, the authors propose that the canonical customer–toolkit dyad in mass customization (MC) should be complemented with user communities. Many companies in various industries have begun to offer their customers the opportunity to design their own products online. The companies provide Web-based MC toolkits that allow customers who prefer individualized products to tailor items such as sneakers, personal computers (PCs), cars, kitchens, cereals, or skis to their specific preferences. Most existing MC toolkits are based on the underlying concept of an isolated, dyadic interaction process between the individual customer and the MC toolkit. Information from external sources is not provided. As a result, most academic research on MC toolkits has focused on this dyadic perspective. The main premise of this paper is that novice MC toolkit users in particular might largely benefit from information given by other customers. Pioneering research shows that customers in the computer gaming and digital music instruments industries are willing to support each other for the sake of efficient toolkit use (e.g., how certain toolkit functions work). Expanding on their work, the present paper provides evidence that peer assistance appears also extremely useful in the two other major phases of the customer's individual self-design process, namely, the development of an initial idea and the evaluation of a preliminary design solution. Two controlled experiments were conducted in which 191 subjects used an MC toolkit to design their own individual skis. The authors found that during the phase of developing an initial idea, having access to other users' designs as potential starting points stimulates the integration of existing solution chunks into the problem-solving process, which indicates more systematic problem-solving behavior. Peer customer input also turned out to have positive effects on the evaluation of preliminary design solutions. Providing other customers' opinions on interim design solutions stimulated favorable problem-solving behavior, namely, the integration of external feedback. The use of these two problem-solving heuristics in turn leads to an improved process outcome—that is, self-designed products that meet the preferences of the customers more effectively (measured in terms of perceived preference fit, purchase intention, and willingness to pay). These findings have important theoretical and managerial implications.