The aim of this paper is to show that the various characteristics of service relationships in public utilities and demands about them require careful thought concerning what we call “activity”. Following task analysis (nurses, office clerks, policemen, funeral directors, crèche, nurses, educators…) don’t do the same work: their aim, the types of interactions between “customers” and workers, work conditions and organization, possibilities of service relations. So, the problem is to precise what aspects of workers’ activities, we have to take into account so that activity analysis can be oriented to a more adequate understanding of the job and relevant ergonomic interventions. In order to take action about health and efficiency, they can often require passing beyond a behavioral analysis which describes effective task or its observable components, according to work conditions. We need to have a better understanding of the internal activity component that is a better understanding of physiological, affective and cognitive mechanisms that direct and regulate this behaviour according to the operators’ motives, goals and possibilities in interaction with the environmental conditions. To render an account of reality, this kind of pragmatic systemic analysis of activity has to be supported by different “activity theories” according to the research purpose and conditions.