The term third sector refers to a set of organizations which are neither capitalist, nor governmental. First of all, this paper aims to extent B. Gui's unitary approach to the third-sector [1991] by focusing on the distinction between third sector and state-owned bodies. Next I propose to translate the non capitalist and the non governmental conditions into operational criteria. I show that these criteria vary according to the nature of the organisations (general interest versus mutual interest). This statement allows me to justify the emergence of two different ways of understanding the third-sector in anglo-saxon and french-speaking traditions.