There is a lot of research devoted to volunteers and volunteering. However, researchers often do not pay attention to a clear definition of the concept of volunteer. Due to the fact that volunteering occurs in a broad context of different situations, there is a problem of generalisation of research results. In order to solve this problem, one must analyse the concept of volunteer. The article describes examples of different approaches to the definition of volunteering, as well as six criteria of volunteering (voluntary action, no rewards, social importance, planned action, longevity, organisational context), carries out an analysis of different situations of volunteering according to the highlighted criteria. There are differences in personality traits of volunteers depending on volunteering area which is illustrated by the research on Russian people helping animals. Comparing Russian and foreign research on volunteers, one has to pay attention to the fact that the foreign definition of volunteering includes