The domain of urban ambiances has developed apace over the past twenty years. It was introduced in order to describe and design the sensory fabric of the urban world more effectively. An ambiance can be provisionally defined as a space-time qualified from a sensory perspective. It involves a socio-aesthetic approach that enables us to grasp everyday urban atmospheres. The aim of this article is to highlight the close links between ambiance and perception. We shall seek to demonstrate that one of the key imperatives for the notion of ambiance is a reappraisal of the situational, sensory, and practical character of perception. Three main arguments are developed: ambiance can be characterized as the quality of a situation, as a motor stimulation, and as a sensory background.