The current explosion in mobile computing and telecommunications technologies holds the potential to transform "everyday" time and space, as well as changes to the rhythms of social institutions. Sociologists are only just beginning to explore what the notion of "mobility" might mean when mediated through computing and communications technologies, and so far, the sociological treatment has been largely theoretical. This article seeks instead to explore how a number of dimensions of time and space are being newly reconstructed through the use of mobile communications technologies in everyday life. The article draws on long-term ethnographic research entitled "The Socio-Technical Shaping of Mobile Multimedia Personal Communications," conducted at the University of Surrey. This research has involved ethnographic fieldwork conducted in a variety of locales and with a number of groups. This research is used here as a resource to explore how mobile communications technologies mediate time in relation to mobile spaces. First the paper offers a review and critique of some of the major sociological approaches to understanding time and space. This review entails a discussion of how social practices and institutions are maintained and/or transformed via mobile technologies. Ethnographic data is used to explore emerging mobile temporalities. Three interconnected domains in mobile time are proposed: rhythms of mobile use, rhythms of mobile use in everyday life, and rhythms of mobility and institutional change. The article argues that while these mobile temporalities are emerging, and offer new ways of acting in and perceiving time and space, the practical construction of mobile time in everyday life remains firmly connected to well-established time-based social practices, whether these be institutional (such as clock time, "work time") or subjective (such as "family time").