Social capital is one of the most polysemic concepts used in contemporary social science. The aim of this paper is to identify the different strategies for defining and measuring the concept with reference to the main theoretical approaches in sociology, namely micro-, macro- and meso-sociological theories. The paper will present the main characteristics of the lexical definitions and the operationalisation of concepts of individual social capital, collective social capital and network social capital. When the different study approaches are analysed, it becomes clear that there is common reference to the more general concept of social relation, although it is reduced to an attribute of individuals in individual social capital and an attribute of collectives in collective social capital. Meso theories are the only ones that manage to preserve the intrinsic relationality of the concept of social capital throughout its operationalisation. Finally, the paper claims that it is not feasible to create any form of fusion between different strategies for defining and carrying out empirical studies on the subject of social capital, as the analysis of social context in each strategy is based on different units.