Sleep has been classically described as an all-or-nothing global phenomenon. However, a growing body of evidence indicates that typical sleep hallmarks, such as slow waves and spindles, occur and are regulated locally. I will present here evidence indicating that slow waves, in particular, may be related with, and offer a read-out of, local and long-range brain connectivity. In fact, slow waves do not only track changes related to both experience-dependent plasticity and brain maturation during development, but also appear to be actively involved in the fine regulation of brain plasticity and in the removal of metabolic wastes. I will also show that, consistent with a local regulation of sleep, slow waves can often occur locally during wakefulness, with an incidence that varies as a function of time spent awake and of previous rest. These waking slow waves are associated with impaired performance during cognitive tasks and may contribute to explain attention lapses and errors commonly associated with insufficient sleep.