A software process is a set of activities needed to transform a user's requirements into a software system. Using a well-defined process is a widely recognized approach to increasing quality and productivity in software development. Building software processes from scratch each time would create high risks and overhead. Therefore, they are often created by tailoring existing processes and standards. Reusing software processes and knowledge embedded in the processes can significantly improve effectiveness and efficiency of software development. In this research, I investigate whether knowledge can improve effectiveness and efficiency of process tailoring and what kind of knowledge can help most in process tailoring. Two types of knowledge are examined, i.e., generalized and contextualized knowledge.