This paper aims to review previous research on the definition of volunteering, and consider the concept of volunteering from the viewpoint of labor theory. The main concern in previous studies has been the nature and effects of volunteering. Previous studies in Japan have been limited to the analysis of the phenomenon of volunteering, while approaches investigating the essence of volunteering have been scarce. As this dearth of approaches represents the fundamental weakness of volunteering studies to date, this study examines the concept of volunteering as defined by labor theory. Labor has the substance of voluntary purposeful relationship movement. In a capitalist society, labor appears as an independent form of wage labor governed by the exchange-value principle. Conversely, the use-value aspect of labor appears in leisure activities. Accordingly, this paper demonstrates that the essence of volunteering is labor based on the use-value principle.