This chapter focuses on engineering-related tasks in the technical development stage. The technical development stage represents the point in the product development process at which a tangible new product emerges or where the specifics of a service to be delivered are determined. Although characterized as a single stage, multiple sets of activities and substages may be conducted within the technical development stage. One of the prevalent themes underlying engineering-related activities during the technical development stage is 'Design for Excellence' (DFX). DFX represents a philosophy in which careful consideration is given to cost-effective operations, distribution, installation, service, and customer use of the product. To facilitate DFX activities, various computer systems exist. These include computer-aided design (CAD), computer-aided manufacturing, and computer-aided engineering. DFX should be recognized as a philosophy that underlies not only engineering-related activities during the technical development stage, but also all departmental activities throughout the entire product development process.