In recent decades, increasing evidence has positioned slow-wave sleep (SWS) as a major actor in neurophysiological phenomena such as glucose metabolism, hormone release, immunity and memory. This proposed role for SWS, coupled with observations of impaired SWS in several pathologies as well as in aging, has led some researchers to implement methods that could specifically enhance SWS. This review aims to gather the current knowledge extending from the cell to the clinic, in order to construct an overview of what is currently known about so-called SWS. We slowly expand the view from the molecular processes underlying SWS to the cell unit and assembly to cortical manifestations. We then describe its role in physiology and cognition to finally assess its association with clinical aspects. Finally, we address practical considerations for several techniques that could be used to manipulate SWS, in order to improve our understanding of SWS and possibly help the development of treatments for SWS clinical disorders.