How do we get voice of the customer? How do we develop product level requirements from them? And, how can we flow these requirements to lower levels? The answer to the first question is in the realm of those with expertise in marketing—and any detailed treatment of the subject is beyond the scope of this work. However, a simplistic answer is that the business needs to first know who its customers are. Are the intended customers other businesses or individuals? Are customers the end-users? By this question, I mean whether the customer would personally use the purchased item or the customer buys on the behalf of a third party. The tools for gaining this information are user studies, surveys and other similar mechanisms. The answers to the second set of questions on developing the product requirements document and requirements flow down to subsystems and assemblies will be explored in this chapter.