When firms involve external partners more actively in their innovation processes, managing knowledge flows across multiple boundaries becomes an important challenge. In this chapter we investigate specifically how organizational, knowledge, and geographical boundaries are bridged by two knowledge integration practices (project management and knowledge matching). We use data from a survey of 415 manufacturing firms on open innovation practices to illustrate how innovation performance relates to the three boundaries that are crossed and how the effects are contingent upon the use of project management and knowledge matching. A main conclusion from the study is that knowledge flows across multiple boundaries in open innovation can be successfully bridged by applying a combination of complementary knowledge integration practices.