Sound quality evaluation applies the results of timbre research to the assessment of the sound quality of manufactured products (domestic appliances, transportation, etc.). This chapter first provides an overview of one methodology. A number of acoustic descriptors reflecting perceived timbre dimensions are established and used to predict users' preference judgements. Whereas such a methodology has proven very effective, it also has some limitations. In fact, most studies only consider the pleasantness of the sounds and often overlook other potential roles of sounds in products and interfaces. In the second part, the chapter introduces sound design. Whereas sound quality evaluation merely proposes a diagnostic of the timbre of existing products, sound design aims to create or modify the timbre of product sounds to meet specific intentions. These intentions consider the pleasantness, but also several other aspects of product sounds: functionality, identity, and ecology. All these aspects are interdependent and often closely related to the temporal and timbral characteristics of the sound. The chapter continues with a discussion of the roles and practices of sound designers and introduces a set of tools that foster communication about timbre between the different participants of a sound design process. In particular, the focus is on the necessity for these participants to share a common timbre vocabulary, and the potential impact of education about sounds is considered. Finally, an important functional aspect of product sound is discussed: how to design the timbre of sounds to support user interactions with the product.