Although the returns of customer participation on new product development (NPD) performance can vary substantially, the current literature lacks a systematic conceptual and empirical integration showing when customer participation is valuable in enhancing NPD performance. Building on knowledge management theory, the authors present a conceptual framework that synthesizes a variety of contingency factors. A meta-analysis empirically examines the moderating effects of contextual factors between customer participation and NPD performance. The analysis reveals that involving customers in the ideation and launch stages of NPD improves new product financial performance directly as well as indirectly through acceleration of time to market, whereas customer participation in the development phase slows down time to market, deteriorating new product financial performance. Furthermore, the benefits of customer participation on NPD performance are greater in technologically turbulent NPD projects, in emerging countries, in low-tech industries, for business customers, and for small firms. The authors discuss several theoretical and managerial implications about when to engage customers in the innovation process.