The paper argues that the notion of ethnolinguistic vitality has been used ambiguously in the vitality theory, denoting three distinct theoretical concepts: sustainability (Su), strength (S) and vitality (V). It is hypothesised that sustainability is a group's ability to continue existing as a group while vitality is its ability to act as a collective entity and strength is its durability in demographic, economic, institutional and cultural terms. It is argued that the sustainability of an ethnolinguistic group is the function of the group's strength and vitality in dealing with the challenges (E) that the natural and social environment of the group poses. According to this model, the crucial factor in this equation is vitality which is the potential for collective action to safeguard the group from environmental challenges. It is further argued that vitality depends directly on social psychological factors that influence the group's shared perception of the interethnic situation. A model is proposed where vitality depends on the perception of the ingroup strength in comparison with outgroups (perceived strength differential), the commitment of its members to the maintenance of the heritage values (U), their cultural distinctiveness and closedness of their social networks (r) as well as the level of perceived intergroup discordance (D). (Contains 1 figure.)