The paper presents the indicator method as an important tool of research in social sciences with the focus on socio-economic geography. It introduces the notion of indicator in the methodological meaning and concentrates on its basic type, i.e. the inferential indicator. The concept of an indicator is explained using a realistic approach, which assumes that unobservable conceptual properties can be represented by observable real properties. In this approach, an indicator is characterised as an observable variable assumed to point to, or estimate, some other unobservable variable. The indicator method is then a way of the realistic conceptualization and a cognitive operation as well. The paper contains the systematization of cognitive indicators in socio-economic geography. It also shows the examples of the construction and interpretation of applied indicators.