This chapter focuses on the openness of the innovation process and the role of knowledge sources in innovation process. Openness of the innovation is the degree to which the process of innovation is open to the external and internal sources of knowledge. External sources enhance search for novel ideas and opportunities for developing new products and practices; internal sources enable the absorption of external knowledge and development of new knowledge. Influences of external and internal information sources could vary across the stages of the innovation process. Absorptive capacity and open innovation, advocating the involvement of external knowledge sources, and structural and behavioral theories, backing the involvement of internal knowledge sources are presented. This is followed by an overview of the studies that have investigated the role of knowledge sources in the innovation process. These studies are augmented by illustrating an empirical study on the relative influence of external and internal knowledge sources on the stages of the innovation adoption process. This is followed by research findings on antecedents and performance consequences of process openness. The chapter ends with implications of innovation process openness for theory and research and proposes ideas for future enquires.